Fast idle on 77 Spider

[Scotsman]

My 77 won't go on fast idle on cold starts. After I keep it going with the throttle it idles nicely when warm. During this warm up, the choke plate opens to vertical so that mechanism seems OK. I am guessing that I have problems with the fast idle screw shown in the pics. Should I try adjusting the depth of the screw or should I try to move the cam to the correct position. If so, how?
Any help greatly appreciated.
Thanks
[img][http://s1341.photobucket.com/component/ ... xu.jpg/img]

If above doesn't work, please try http://s1341.photobucket.com/user/Ediscot/library

[bradartigue]

If it is engaging on the cam and the cam is turning "on" when cold and "off" when hot then adjust the screw to set the idle. You have to adjust it with the cam fully "on" so that the engine runs around 1000 RPM and when "off" it should disengage fully and run at 850 RPM.

Your idle speed must be set right when hot before you set this thing, so make sure it is.

[Scotsman]

Brad

Many thanks for your info.

Did as you said and now have fast idle about 1100 that kicks off to normal idle about 850. l also have regained regulation with the idle mix screw at long last. My only concern now is an occasional pause and drop in revs when going quickly from idle. Hope I don't still have acceleration linkage issues as Roy suggested but won't know until I make final adjustments after a drive. Hope to hit the road soon to check this out.

Thanks again.

[bradartigue]

Brad

Many thanks for your info.

Did as you said and now have fast idle about 1100 that kicks off to normal idle about 850. l also have regained regulation with the idle mix screw at long last. My only concern now is an occasional pause and drop in revs when going quickly from idle. Hope I don't still have acceleration linkage issues as Roy suggested but won't know until I make final adjustments after a drive. Hope to hit the road soon to check this out.

Thanks again.

That sounds like an accelerator pump problem, it either isn't engaging (the roller arm is bent) or the diaphragm/spring aren't working.

[Scotsman]

Took it for a ride. Engine Idled smoothly near 850 after warm up. Ran nicely, good response to throttle , no backfires . Thought I had fixed my carb problems . ALAS after a few miles, when I slowed quickly for stops, the revs crashed and fluctuated between 200 and 400 and/or engine cut out. Started back up immediately, but problem persisted. Had to readjust idle speed screw back to normal once I made it home.

Could this also be due to an accelerator pump problem you suggested for the pauses on quick throttle increases? I had replaced the diaphragm when replacing the float but will take the carb off again for a look. Is there any test I can make to be sure the diaphragm is working properly before I put carb back?

Thanks.

[Scotsman]

I had a look at accelerater link as suggested by Roy and Brad. Looks like they hit it on the head. The roller is not in contact with the cam as shown, hopefully, here. The cam touches the roller when I push the throttle linkage fully forward but does not engage or touch it when I release.

How do I reset this linkage? Can I do this without taking the carb off again?

Many Thanks
[img]iPad[/img]

[Scotsman]

Sorry, pic didn't post.
Trying again
[img][URL=http://s1341.photobucket.com/user/Edisc ... d.jpg.html][IMG]

[RoyBatty]

Posting these images for the OP.

[bradartigue]

It is way off, like the arm is bent or the accelerator pump was assembled wrong. You can disassemble the pump in place, just undo the four screws holding it together. The cover and spring and diaphragm will come apart. Figure out why it won't touch the arm with the roller. I can only think the spring is missing or the arm is bent badly.

[Scotsman]

Yes, I screwed up installation of the spring. Now it is correct, roller is in touch with cam and I have good responses with fast throttle up or down. The engine idles very smoothly on fast idle about 1100 when first started and kicks off to low speed idle. Bad news is the low speed idle now jumps around between 2-850 even with warm engine and I have lost regulation with the idle mix screw. Previously I had been able to stop the engine with the last half turn of the idle mix screw before it seated but I never had the fine control described by Brad. Now the engine still runs, though poorly, when screw is fully seated. What have I screwed up now?

I have replaced float, needle and diaphragm, cleaned jets and replaced the idle mix screw and O ring. When I removed this screw the O ring was in the groove nearer the screw head as shown here, I hope
[img][/[IMG]http://i1341.photobucket.com/albums/o759/Ediscot/60de904d-e363-401a-b775-d79aa07b3cd2_zpsdsdi5v9n.jpg[/img]img]

Is this correct?

Can I have another internal leak? I find no external leaks by spraying with carb cleaner.

Any suggestions would be welcome.
Thanks

[bradartigue]

The mix screw looks right.

Wavering idle means you have an air leak somewhere.

[Scotsman]

Brad

Can't find air leak with lots and lots of carb cleaner spray but will keep looking.

Would you please tell me if theses hoses near the idle screw mix are properly connected? The upper left goes to the inlet manifold, the RH to the fast idle deceleration system. The air pump has been disconnected but hoses and valves remain. It terminates at two connections near the1 and 4 spark plugs.

Thanks

[bradartigue]

I don't think that lower one is for fast idle.

I would plug everything except the fuel lines and tune it. This includes the electronic distributor (if you have one) and any air line (brake booster) connected to the intake manifold. Then reconnect things one at a time and tune. When you find it wavering you've found your issue.

[707kevin]

The lower right line should go to the top of the charcoal canister. Yes??

[Scotsman]

Kevin

I had the lines reversed from the charcoal canister as you thought . Also found and fixed a small air leak. Back on the road again. Thanks again.