solex carbs/throtle

[jbeachx356]

i just got a 67 912 with original solex carbs and although the carbs have been professionally tuned and adjusted, they still have a problem idling smoothely. when i am stopped, the idle bounces around anywhere from 400 all the way up to almost 3000, and the idle will go up all by itself even when i have my foot off the pedal. it seems that it might be that my throttle linkage is stiff and that it is not releasing all the way or that the spring on it is worn out, something to that extent. anybody have any ideas on what might be causing the idle to jump up and down? thanks jimmy

[Jones Low]

Assuming your carbs were rebuilt correctly and your ignition system is in good/new shape, the next thing to do is to adjust idle and balance the four carb so that they are drawing evenly at idle. Learn to use an unisych or similar device for balancing the carbs. The throttle shaft may need to be twisted (solid shaft) or adjusted (split shaft). Another area is a ignition distributor that has bad weight springs in the mech. advance or a leaky vacuum line in the vacuum advance (I don't think you have a vacuum advance in a 66 though but check anyway). Also check for manifold leaks.

You disconnect the leakage from the carbs and have someone step on accelerator pedal while you check in the back for binding.

Good luck.

jl, 69-912

[Ran Hanks]

I am glad I am not the only one who is having throttle problems. I just dropped 2500 dollars into an engine rebuild and carb rebuild and I am having the same problems I had before. I took my 68 back to the shop and made the suggestions that were suggested by JL. They are working on it now and I will let you know what they did.

Ran

[Jones Low]

Jimmy & Ran,

How goes the carb balancing and throttle adjustments? Here are some things I had to do:

Once I got the carbs somewhat balanced, timing right, and idle adjusted somewhat correctly, it was still not right yet. I ended up running the car without the air filter canisters/housings. I know it's not good for the engine to run with unfiltered air but I was still trying to get the carbs to balance (they would pop and backfire a little). For this short time, a few hours on a Saturday morning, I spent driving the car, stopping and adjusting the carbs using an Uni-synch several times until everything seemed to be right. I'd make an adjustment and then run the car. Make another adjustment and run, etc. Low and behold with a little patience the engine started to running better than before. Don't give up. There are minute adjustments that can be made and the right combinations can be zeroed in. It just takes a little time.

By the way, make sure valves are adjusted correctly, plugs and points are in good condition, and timing is correct.

Balancing the carbs is an art form that takes time to learn. Most of the learning is through trial and error. Let me know how your trials and errors turn out. Happy to share my experience with my 912.

jl, 69-912

[Ran Hanks]

Seems like everything was balanced and tuned. What made the difference was a new distributer. They put a .009 on and it runs like a top. I told them I wanted the .050 and they said they would swap it out when I brought it back in after 300 miles. I know we have already hashed through this but it runs so well now. What will I gain by replacing the .009 with the .050? I can do 70 in third gear at just over 5000 rpm. Is this average, better than average, where do I stand?

Ran

[Jones Low]

Ran,

Glad to hear your engine is running great. Check out the discussions on the 912 Registry
(www.912registry.org) under Technical Information, Ignition System talks about pros and cons regarding .009 and .050.

Jones Low
69-912

[Ran Hanks]

I guess I jumped the gun. I am still having problems with backfire, sporadic idle, and the engine sputtering to a stop at intersections. The mechanic at the shop said they (the carbs) were as good as they were going to get. I can't believe after spending $2500. dollars on a top half engine rebuild I would have the same problem I had before. I am going to take it back again, any advice on what I should tell them to look for or do? I am at my wits end.

Ran

[yarbe]

have you checked to see if you have a two piece throttle shaft? the adjustment block
between the bores sometimes falls out. that won't make it sputter, but sure gives you an erratic idle. the front throttle butterfly would be free to open and close on it's own.