# Help! Solex side draft idle range issues



## joezeeuw (Feb 23, 2003)

Hi experts,
You might have seen my posts of random questions regarding counterflow carbs but I have hit a wall here and I need some one-on-several diagnostic assistance. I was on track trying to get this thing to H2O but time is slipping away.
Here's what we are working with:
1.8L 8v
JH head (rebuilt)
Basically stock except for a cam of some sort.
Solex ADDHE40's (rebuilt)
Points ignition w/vac advance
Sorry I don't have the jetting info in front of me but I'll get it
Basically It runs awesome when not on the idle range but when the throttle plates close it backfires like a mofo but not all that consistently.
Here's how it usually goes:
You start it up and you can get it to idle decent but the speed screws have to be like 3 or so turns from closed. You can rev it and drive it but it backfires through the exhaust like I said. I've synched the carbs to perfection and messed with the idle mixture to no end in this stage with no change.
Here's where things get weird: If you drive it for awhile longer or let it idle you can have it at idle and all of a sudden a change occurs. The idle speed gradually picks up to around 2500. This is with no change of adjustments mind you. It starts backfiring in the same manner as before. Once it gets to this stage you can back the idle speed screws off until around one turn from closed. I have a CO meter that only seems to work when it wants to but I had it working briefly and found I can get 2%CO with the idle mixture screws 7 turns from seated. With these settings it actually runs pretty good and still backfires through the exhaust a little but not too bad.
So that's when in the past I've said OK lets shut it down and see how it does cold. Well cold it won't idle unless the speed screws are way in as I mentioned. So basically it goes from one, we'll call it a phase, to the other. I can sort of tune it to one but then when it's in the other it runs like poo. I'm not talking about a switch from cold to operating temperature here either. It is well after the t-stat has opened and the transition can happen within like 15 seconds.
OK things it isn't:
The engine. I've done a compression and leak down test, reset valve lash twice, check cam timing again and again. 
Ignition timing. Set at 6 degrees at the correct mark. New points and gap set with feeler. I ran this very setup with the previous motor with zero issue. I had suspected briefly that the timing was running away but once I get the idle to settle down in "phase two" it is fine so we have the same timing with a difference in idle speed screws of two turns with the same idle speed. If the timing was running away I should be able to bring the idle speed back down but then it would need the same idle speed and mixture settings to run the same.
Exhaust leak. Nope
Intake leak. I smoke tested each runner. Zero leaks at the soft mounts or manifold. Some leakage at the throttle shafts, I'll get to that later
Fuel pressure. This is an issue that had me side tracked for some time. I'm running a Carter 4070. I ran this same setup on my previous setup with zero issues. With this setup however the pressure would start to drop after awhile and eventually hit zero. I tried freaking *every* variation on plumbing configurations and three different pumps. The only thing I could get to work was running it as a return style setup. It seemed like the pump was somehow getting air in it. Running a return allowed it to always have a fresh stream of fuel rather than just trying to push the same bunch of fuel. Right now I have the return regulated with a pair of vice grips but it's holding a solid 4 psi with no change in the running condition (Ive tried other pressures from 1-6 psi with no change as well).
Idle mixture/synch/linkage. I've fiddled with this stuff for hours. Slight improvements can be made but it doesn't seem to be addressing the core issue.
Fuel contamination/clogged passages/ etc. In addition to initially rebuilding the carbs I've had them apart twice and blasted every jet, passage, and venturi and checked every o-ring.
OK. On to my theories/possible explanations:
#1 Boiling fuel. From what I understand this will cause the float to drop and the car to run rich. Well that would certainly cause a backfire but I don't see it bumping up the engine speed unless there was some weird emulsification going on or something. I've run the car with a fan blasting the carbs with no change. With the switch to a bypass style fuel supply the carbs have a constant supply of cool fuel, no change. People have been running setup similar to this without a return without any weirdness like this. Still, I can't prove that it *isn't * happening so I have not ruled it out.
#2 Worn throttle shafts/butterflies. As I stated earlier when I smoke checked the intake there was a decent amount of flow through the throttle shafts. There isn't a whole ton of play in the the actual bearings though. There does however seem to be an excessive amount of side to side movement in the shaft like the butterflies have worn against the carb bodies to the point that the bore is slightly out of round. This could certainly cause an incontinent idle and depending upon where the plate is it could cause airflow across progression holes, cause weird vacuum issues and generally make the idle weird. However, I don't see it causing such a drastic change. Plus, I can push the shaft from side to side (it's quite slight BTW) and it doesn't change the way it runs.
Whew well I didn't intend this to be so long winded but if nothing else it allowed me to get my thoughts in order. A logical next step would be to substitute another set of carbs but I don't really have a ton of cash or any at my immediate disposal. I've been busting my ass trying to get this thing to H2O but it's making me look like a jackass. Any insight would be greatly appreciated.
TIA
Joe
PFV










_Modified by joezeeuw at 10:50 PM 9-14-2008_


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## candm (Apr 27, 2003)

*Re: Help! Solex side draft idle range issues (joezeeuw)*

3 things. timing should be more at idle, say 10-12. also, at least on my webers, back off both idle screws, main and second, tighten the main one till it just hits the lever, tighten the second one till it just hits the lever, now back to your main one no more than a 1/2 turn. of course you then need to sync them with slight changes but you mentioned that you were 3 turns out which means you are cheating the idle circuit by exposing the progression holes past the throttle plates and richening the mixture- possible air leak or too lean of an idle jet. also i have the carter 4070 mounted by the tank with a regulator in the engine bay. no problems. some say to use a return line but ferarri and alpha romeo, just to name a few, used these carbs for years as standard equipment with no return. good luck


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## joezeeuw (Feb 23, 2003)

*Re: Help! Solex side draft idle range issues (candm)*

When you say main and second what are you referring to?
For each carb I have an idle speed screw which opens the butterflys and I have a idle mixture which opens a passage for fuel.


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## B4S (Apr 16, 2003)

*Re: Help! Solex side draft idle range issues (joezeeuw)*

I have the other style of carb balancer on my setup, the one that joins them in the center of both. I was having similar problems to yours, but a bit more intermittant and not consistent at all. One day I was poking around and the arm that joined left carb to right carb FELL OFF! Turns out that it was wiggling around, and sometimes the left carb would close completely, sometimes it wouldn't. Physically playing with it made no change to the way the car ran, but sure enough when I fixed it, all problems went away. I'd DEFINITELY suspect that the leaky bearing is an issue, especially if it changes 'tune' after warming up. Heat might be swelling the bearing shut so it's behaving like it should.


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## joezeeuw (Feb 23, 2003)

*Re: Help! Solex side draft idle range issues (B4S)*

I've tested it with the linkage completely disconnected so I'm pretty sure it isn't a linkage issue.
Can I borrow your carbs for a few days.


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## candm (Apr 27, 2003)

*Re: Help! Solex side draft idle range issues (B4S)*

i have an interconnecting throttle linkage which uses 1 idle speed screw as your main idle adjust and a secondary srew to balance the other carb. sorry, yours is different. still, make absolutely sure your linkage setup connecting the carbs is not sticking and i am not sure with solex carbs but on weber sidedrafts, your idle speed screws, not mixture, should be no more than1/4-1/2 turn out to achieve your idle speed. you mentioned you are out 3 turns and i doubt the solexs should be near that


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## joezeeuw (Feb 23, 2003)

*Re: Help! Solex side draft idle range issues (candm)*

Well I convinced my boss to let me scrounge through his old weber parts. I was able to piece together a set of 40's. With just a base setup I could tell an immediate improvement. It had it pretty well dialed in within 10 min. Same linkage. Running damn nice now with just a best guess set of jets. I wish I knew exactly what the deal is with the Solex's. Perhaps they were just plain worn out. I fully agree that 3 turns is not right but it was the only way to get it to idle when it was acting in that manner. I'm glad I can finally move forward. Maybe later I'll go back and see if I can get the Solex's running OK.
Thanks for the help everyone.


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## tobiwonkonobi (Nov 18, 2002)

*Re: Help! Solex side draft idle range issues (joezeeuw)*

glad to see you got it sorted and hope to see it in a few weeks


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