[johnbran]

Thanks for all the information. Now I have a few other questions on this. I've noticed that my GT will run smooth as can be sometimes, and other times it will run rough and want to pop and backfire at first when I attempt to rev it up, but then it will usually get to a point where it smooths out and revs on up. I doubt that this would be the valves or it would do it all the time. I'm running the origional Solex carb, which I know most people will say that's the first problem, but I have rebuilt the carb and replaced the vacuum lines that looked rotten. Also, if I let it set overnight, I always have to prime the carb with a shot or two of gas to get fuel to pull up to the carb. Once I get it started the first time, it will start all day long until it sits for several hours or overnight. I've checked the lines to the fuel pump and they are not plugged and I pulled the cover off of the fuel pump and cleaned out what little debris there was accumulated in it. I have noticed that the two middle screws that secure the top plate of the carb to the middle body are loose and do not want to tighten up due to the holes being stripped out, so I figured this could be causing a vacuum leak, but I didn't know if this would cause the problems I'm experiencing. Could these two problems be related to each other or are they more than likely two seperate problems? Either way, does anyone have any suggestions about correcting these problems? I haven't removed the fuel pump entirely or completely disassembled it yet. I've heard people talking about the pumps getting gummed up inside after sitting for a while, but once I get fuel to the carb, it seems to run fine. Well, except for the occasional rough running and backfiring. If any of you out there have any suggestions on this, I'd really like to hear them. Thanks again everyone!

John

 

[chuckspeed]

'Kay...

While you're on the right track, the real culprit is the choke.

Remember, you're driving a 30+ year old car - they don't run like digitally controlled, fuel injected motors. Back in the day, we used to have to 'warm up' a motor before leaving the driveway...a minute or two to get some heat into the motor was essential to prevent hesitation, backfiring, and stalling.

Here's what happens:

Fuel must be properly atomized to ignite and burn. In a cold motor, fuel does not atomize properly - it drops out of its air suspension, leaving a lean mix for Mr. Sparkplug to light off. On an FI motor, the injector does a good job of getting fuel atomized - plus there's less time for it to drop out on a port-fuel injected system.

Carburetors, on the other hand, rely in differential vacuum for atomization. This is all well and good when warm - Opels rely on a little heat exchanger between the intake and exhaust manifold to keep fuel atomized. This is the section directly under the carb where the two manifolds are bolted together.

When cold, fuel has a long way to go before getting lit off. It WILL drop out of suspension. When it does, the mix will either light slowly, light late, or not light at all. This is the stumbling and backfiring you speak of. The solution?

The choke.

This extra plate 'amplifies' the vacuum signal, causing additional fuel to be pulled into the motor. There's also a set of linkages which step up the idle speed - all of this has to be set up properly to prevent the dread backfire stall. On a properly set-up motor, ONE 3/4th pump of the accelerator is needed on a stone-cold motor to provide a pump shot AND close the choke linkage to start. Said stone cold motor will then light off. Left on the highest choke setting, the motor will idle slightly above stock idle (1200 RPM) right off, then GRADUALLY increase in idle as the motor warms up. If you leave it on the hight setting, it should eventually make it to *about* 2200 RPM. A quick 'blip' of the accelerator releases the linkage, and the idle drops to the stock happy burble.

FWIW, I'm a big advocate of the water choke. This choke uses coolant temp to regulate the choke plate - a direct relationship between the motor temp and choke setting. Later Opels (late '72 thru '74) used an electric choke - I always had problems synching the choke with the motor. By retrofitting the water choke, said prob goes away.

Maggie the Opel lights off just the way I described above. Getting the choke settings right go a long ways towards improving the Opel experience...

 

[johnbran]

Thanks for the info chuck. I only have a few questions about it though. I understand how the choke may be responsible for the backfiring when the engine is cold, but sometimes it will run fine even cold and then start the backfiring after it is up to running temperature. And then sometimes it is the complete opposite and runs rough when it's cold. Sometimes it will run smooth the whole time and not backfire hot or cold. Does this sound like something that could still be caused by the choke? I know that the choke is not quite adjusted properly, but it seems to run fine cold part of the time. As I have said, this is my first Opel and I am not very familiar with their quirks, but I have been told numerous times that they are very tempermental about vacuum and any little leak can wreak havoc on how the engine runs. That is why I have suspected a vacuum leak somewhere. Could there be a vacuum leak between the two manifolds as I have heard some people talk about? If so, how would I go about checking for this? I thought of trying an old Chevy V8 trick and spray some WD-40 or carb cleaner around where the two meet and see if it speeds up the idle or slows it down, but I didn't know if this would even work on this type of setup. Is there any good ways to check for vacuum leaks in the system with any kind of accuracy?
Also, would you have any ideas why the fuel seems to drain back to the tank or evaporate out of the carb every time it sits overnight? I've tried working the throttle linkage while looking down the throat of the carb and it doesn't even attempt to spray any fuel down the carb. It's like the carb completely drains of fuel after sitting. So, every time I go to start it after sitting for several hours or overnight, I have to prime it with a few shots of gas to get the fuel back up to the carb. Once it gets the fuel to the carb, it will start fine the rest of the day as long as it doesn't sit for more than a few hours. Have you ever had this problem or know of what I should check? I origionally thought the fuel pump was bad, but like I said, once I got fuel up to the carb, the pump works fine with plenty of flow. This one has me completely stumped at this point, so any info you or some of the other members can pass along would be greatly appreciated. Sorry this has been another long post.

Thanks, John

 

[chuckspeed]

I'm sorry - I misunderstood.

The weakest link of the powertrain on an Opel is the carb. There are three primary problems with it:

1. FLOAT LOGGING

The float is a foam piece which was never really intended for the fuel additives we now use. Over the years, this foamie float will absorb fuel and get 'heavy' in the float chamber, thus increasing the float level. The result is poor fuel economy, loaded plugs and poor idle quality.

The fix? A new float - not available anymore. The other fix is to dry out the float (long periods of sun drying) and a coat of sealer, but this is a so-so fix. The float will always be heavier than NOS.

2. LOOSE BRASS BITS

ALL the brass parts of a Solex eventually attempt to escape the carb body at one point or another. The engine vibration, coupled with heat cycling, cause the parts to loosen. The dangerous one is the fuel inlet tube - when it starts to leak, it dumps fuel onto the exhaust manifold. Not a good thing - a recipe for an engine fire! The solution is to have these brass bits knurled and re-insert them with some fuel-resistant sealant/adhesive.

3. HEAT WARPING

The Solex has a really thin material cross-section, which allows the carb body to warp as it is thermally cycled. The effect of warping is exacerbated by VERY thin gaskets, and few bolts holding the whole schmeer together (pre '73 carbs).

The two areas to check are between the airhorn (top) and the carb body (venturi and float bowl) and between the carb body and throttle body. If the carb body is warped (95% chance it is), the fuel will find a way out - I forget the leak path off the top of my head. This is what is probably happening to you. The solution is to re-face the three pieces by milling, then use the thicker gaskets typically supplied in carb rebuild kits.

Chances are you have all three things going on at the same time - keep in mind the motor is real sensitive to sparkplugs and timing, too. It has to be *just* so to work right - more sensitive than a SB Chevy.

Okay - that's the long answer.

The short answer is to buy the Weber conversion. Better starting, better idle quality, more power, and better fuel economy. More expensive, too.

It is possible to get the Solex to work right, but it's a tremendous amount of work. Most folks ante up for the Weber and drive...

 

[johnbran]

Thanks chuck,
I think that you may have just hit on the source of my problem that I have suspected for some time. The two center screws that hold the top airhorn to the center body on my carb are mostly stripped out and will no longer properly tighten down. From what you've informed me of here, I'd just about bet money that the problem is due to a leak between the top and middle body due to these stripped screws. Luckily, I just bought another complete solex carb off of ebay last week with the intention of replacing the center body of mine and I should have it here by the end of this week. The carb is supposed to be complete and usable, so depending on how it looks, I'll either stick it right on and try it, or I'll take the best parts from the two carbs and make one good one (if that's possible out of a solex). I'll try checking the flatness of the mounting surfaces while it is apart and see if there is any warpage going on before I stick it all back together and give it a try. I had forgotten something I did a while back to attempt to narrow down the problem. I stuck one of my good running chevette carbs on the GT to see how it ran and it ran like a top with no backfiring or missing and would idle without missing a beat all day long. So, this pretty much told me the problem was in the carb, but I had no idea what to check for with one of these. I thought of just leaving the chevette carb on it, but it would have been a lot of work to change the throttle over to a cable style, get the hood clearance needed for the air cleaner, and re-wiring the harness for an electric choke since my solex has what I believe is a water choke. Which by the way, makes me think of another question which may be really dumb. Sorry, I know this is already too long, but here goes. Is the water coolant actually circulated through the round housing of the choke through the two tubes coming out of the cover and if so, where are the water lines for the water choke supposed to come from? I cannot find any small water lines that will fit the choke fittings anywhere under the hood, so I'm assuming my choke is not working correctly or not at all. If water lines do not connect to these tubes, what does? As I said, this may be a really dumb question, but I'm learning as I go on this thing. Sorry this has turned into such a long post again. I'll try to keep it shorter next time. Thanks again for all the help chuck. You really have helped me out a lot.

Thanks,
John

 

[oldopelguy]

"T"

There are supposed to be a couple of "T"s in the heater hoses that supply water to the choke, and yes it is coolant.

There are several different Solex carb's out there, with varing levels of interchangability. The hardest part is the GT to non-GT mix because GT's have mechanical secondaries wheras Mantas and Kadetts have vacuum secondaties for the most part. Let me know if you can't make it work and you still want a Solex, I might have a useable one laying around, or if not I do know I have 20-25 carbs worth of parts and I can probably get the part you need for one.

If the fuel is actually draining out of the carb while it sits, do a quick check next time you start it. Disconnect the hose at the carb and see if there is fuel at the hose. Sometimes fuel pump check-valves don't seal all that well and let the fuel gravity drain back. If there is fuel there, get a flash light and remove the air cleaner cover from the carb, open the throttle and choke all the way, and see if you can see a shiny puddle in the bottom of the intake manifold. If the gas is indeed inside the manifold, we need to fix or replace that carb.

Good luck.

 

[johnbran]

Thanks for more great info. As for your suggestion, I've looked down the throat of the carb after it has sat overnight and it appears to be bone dry in there. I've worked the throttle by hand to see if it will spray any fuel into the intake after sitting and it won' t even attempt to spit out any fuel, so I'm assuming that the bowl is completely draining off while it sits. Also, I've tried hand choking the carb (holding my hand completely over the airhorn) in an attempt to get it to overchoke and pull gas to the carb, but this does nothing. The only thing that gets it running again is pouring a few shots of gas down the throat of the carb and starting it up. I usually have to do this several times before it will pick up the gas and run on it's own, but once it finally picks up fuel, it will start and run all day long if it doesn't sit for any extended period of time without being started. I tried to do this by spraying starting fluid into the air cleaner pickup to save having to remove the air cleaner from the carb, but this dried out the cylinders and made the motor knock like crazy for several seconds and I decided it was not worth saving a few minutes if it was going to hurt the engine. So, how would I go about checking the check valves in the fuel pump? I've got an extra fuel pump that came with the car, but it doesn't look too healthy. Do these pumps come apart to clean or rebuild them. I have seen some advertised that do, but I don't know if the GT's had this type or not. As for getting a new carb, I now have three and I just bought another used one that should be here any day now. Also, I've completely rebuilt the one that I am running now and took what looked to be the best parts from each. So, I'm assuming that my next step will be to investigate the fuel pump a little closer????

On the water choke subject, the fact that it is missing the "t's" for the choke hoses is not too surprising. I had noticed that the heater hoses are not running to the heater core and just make a loop through the radiator and motor. And if the coolant fills the choke housing, what about the small hole in the bottom of it? All three of my carbs have a hole about the size of a pencil lead in the bottom of the housing that I would think would make the coolant just leak right out of it. Or am I taking this information the wrong way? Also, the heater control valve (which is still mounted to the pass. wheel well with short pieces of rotten hose stuck to it) has rusted shut or froze up in some way, so that is going to have to be replaced when I re-run the heater hoses. Does anyone know if a standard ball valve or shut off valve from the local hardware store will work for this, or do I have to try and track down an origional opel valve to make it work right?

Gee, so much for not making another long post. Sorry everyone. But you can't get good quality answers without good quality information, right?

Thanks again, John

 

[chuckspeed]

Okay.

The three big variants in opel carbs are:

Mech secondaries vs vacuum secondaries (as oldopelguy said)
Waterchoke vs. electric choke (a late '72 change)
5 bolt vs 7 bolt airhorn (73-74 change)

The best running setup (for me, at least) is the 7-bolt airhorn, the water choke, and the vacuum secondary. I've never been able to understand why one body style had mech and the other vacuum when they all weigh within a few hundred pounds of each other - the vacuum secondary has a much smoother throttle response.

The 5 bolt airhorn carbs are prone to strippage. In the short term, it's possible to tap the bolt holes to accept a US screw thread - if forget which size it is, but there is a screw a bit larger than a metric which will work.

Your fuel is NOT leaking back into the fuel system. The float needle in the airhorn acts as a siphon break, preventing the fuel loss you speak of. The fuel is leaking out of the bowl between the main body and the throttle body - it's been a while since I've had to rebuild one, so I don't remember the exact leak path. It's there, tho.

As for the choke -

The water circs thru a cavity in the front section of the choke. The adjacent section (the one with the hole) has a bimetal strip in it - this is what does the work of moving the choke plate. The water choke is set up to circ coolant thru the supply and return heater core hoses - there should be a pair of tees in the lines running back to the heater core at approx cyl #3.

The control valve -

Sure! A ball valve will work fine with a pair of hose adapters screwed into it. The 'trick' to getting it to work is to weld an offset to the ball valve handle. Drill a small hole in the offset, and connect a lawnmower throttle cable to it and you HVAC controls in the car. I've done this on more than one car, and it solves the problem of the poppet valve for good!

 

[johnbran]

Thanks for the details chuck. With the great info I've gotten from all of you, I think I know what I have to do to fix this thing finally. You all are probably glad to hear that so we can get off this subject, huh? I'm sure it won't be the last question I'll have during this project, but I really appreciate all the help from everyone on this particular topic. I really did learn alot.

Thanks again everyone,
John

 

[chuckspeed]

John-

S'okay. You're welcome.

Back in the day, my friends thought I was crazy for not working on SB Chevys and Ford Windsor motors - Thought they were kinda boring on account of everyone else did them. The Opel was different - even more so today.

It's nice to know that there's a place where this accumulated knowledge can be shared. While I'm no Rally Bob (nor would I ever claim to be a distant second) I do enjoy helping others avoid some of the pitfalls and frustrations I had to work thru - like figuring out how to get the motor out the very first time (you pull the car - not the motor).

I always wondered if there would ever be a chance to 'download' the experience - now I know.

Motor on, guys!

 

[Gary]

I always wondered if there would ever be a chance to 'download' the experience - now I know.

Motor on, guys!

Once the "'Super FAQ" module is up, you will have your wish, chuckspeed!

 

[johnbran]

Just thought I would post an update on the carb situation. I thought I had everything lined out on my carb, but when I went out to work on it today, I had the same problem as before. It just cranked and cranked and acted like it didn't have any fuel. I received the other carb a few days ago that I bought for a replacement, so I decided to pull my rebuilt carb off and stick the other one on. Well, as you suspected guys, the intake had a puddle of fuel lying in it where the fuel had leaked out between the carb sections. I thought I had the problem fixed by re-tapping the two stripped center screws, but apparently not. Anyway, I replaced the problem carb with the one I just got and you would not believe the difference! Yes, it's still a Solex, but this one works. I thought it ran good with my rebuilt carb (at times), but this carb made it seem like I stuck in an entirely different engine! The missing and backfiring are completely gone, it starts right up in less than half a crank, and it pulls strong all through the RPM range. Not too shabby for a $6 carb (ebay, of course). Best of all, I let it sit for about 8 hours, which would have required priming the old carb, and it fires right up without even hesitating. So now I can concentrate on the next phase of the project.......Brakes and steering. But that's an entirely different set of questions.

Thanks again for all the help everyone,
John

 

[chuckspeed]

always a pleasure.

Keep that old solex - before yo know it, you'll have a stack of them just like everyone else!

 

[RallyBob]

I used to use my old Solex's as wheel chocks.....
I like them so much, I'm the one who suggested the 'Solex Shotput' at the OMC's annual picnic. Popular event I hear!

Bob

 

[chuckspeed]

there's a thread...

101 uses for a dead Solex.

 

[johnbran]

Flaming GT anyone??

Well, the GT is running and starting great with the new Solex, but I've still got one problem. I have fuel slowly dripping from the fuel line inlet on the carb. I tried changing the fuel line in case it was cracked or split, but this did nothing to stop the leak. From the looks of it, the fuel is actually coming out around the base of the brass insert that the fuel line attaches to. I take it that this is yet another defect in the wonderful Solex? How about fixing it? Any ideas or tips? Would silicone seal the leak up on this or is there a more "permanent" fix that can be done? It really doesn't affect the way the engine runs, but I just seem to have a problem with running raw fuel down onto the exhaust. Just doesn't look like a good idea. So if anyone out there knows of a more permanent fix up for this than just smearing some silicone around it, I'd really like to hear about it.

Thanks,
John

 

[chuckspeed]

John-

Silicone won't get it.

The prob is defined as 'loose brass bits' in the thread above.

To permanently fix it - pull the fitting, knurl it, and lay a thin film of epoxy on the exterior of the fitting before sending it home with a soft mallet.

 

[oldopelguy]

Lazy man

2 more options to fix the brass inlet being loose:

Grab it and remove it with a pair of vice grips. Then, with the top off the carb and the needle and seat removed, drill and tap the hole for a barbed pipe fitting. With the proper pipe thread tap you shouldn't need teflon tape, but you can use it if necessary.

My personal favorite: Remove the top of the carb and completely strip it of everything that will come off including the inlet tube if you can remove it without damaging it. THOROUGHLY clean the top of the carb and the inlet tube, first with a degreaser or carb cleaner, then with dishsoap and water to remove the carb cleaner. (It isn't clean until your wife can stand the smell of it.) Reinstall the tube into the carb top. Wrap the top of the carb in aluminum foil and bake it at 350 for about 20 min. Carefully remove the very hot carb top and, while it is still hot, apply some plumbing solder to the joint where the brass meets the pot metal. The solder *should* melt and flow right into the joint. Let it cool completely and reassemble. My father has an oven in the shop and we've used this method on scores of old carbs, without a single one requiring rework. The oven method works better than a torch at keeping the pot metal from warping, and there is little risk of fire if the parts are thoroughly cleaned.

I, however, will not at all, now or ever, accept responsibility or be accountable for the fire that may ensue if I do not personaly clean the carb.

 

[chuckspeed]

wow.

That's a great way of doing it! I never thought of that!

 

[opelmark]

That IS a good one, & I especially like the disclaimer at the end of the post. Sounds like the legal dept. at work. Hey, it's a litigious world . . . one thing to add: sometimes fuel & teflon tape aren't compatible--it's not recommended in nitrous installations for similar reasons--so, if it's necessary, you might want to use thread sealing paste instead. OR, John, you could just buy yourself a Weber 32/36, the leaking Solex becomes your new wheelchock/paperweight/whatever, & you have fewer carburetion problems in the future. Of course, this is only the opinion of 99 percent of Opelers worldwide, so I suppose we could ALL be wrong.