56 replies to this topic

[Shifty]

Have you got the correct fuel cap on the car or is the vent pipe blocked?

What do the plugs look like?

Can you do a compression test?

Does the carb piston rise and fall easily(did you centre the jet after changing it?)

Have you tried advancing the timing as it could be way to retarded?

[80sMiniCity]

Thanks for everyone’s help in solving this issue. Here’s the current situation. I put 20 weight oil in and only one red spring. When I rev the engine, no load, and the piston starts to rise the revs drop and the engine wants to stall. The piston rises a little (about 3mm) and the revs drop and the piston doesn’t rise anymore for about 2-3 seconds. I’m assuming when it finally builds some vacuum the piston starts rising again, the engine revs good above 3000 rpm.

So I turned the jet adjusting nut all the way in and then backed off 12 flats. The car would not start. I had to turn it an additional 12 flats to get it started. I’m assuming there’s something wrong with the fixed jet I put in. So the HS4 is off the car.

I’m going to switch back to the waxstat jet and see what happens. The only needle I have is the aaa spring loaded. Can you use a spring loaded needle in a fixed jet? Maybe that’s the problem.

[blacktulip]

have you not got another carb you could try? or a friend with one?

[mk1leg]

Sounds like you have a too bigger carb for a 998cc.....and what cam are you using.........is it a modern profile 265,275,285, or an older type profile 731,546,649........a strange problem........can you take a vid of the problem so we can diagnose it......

[Shifty]

Just a thought but have you check the thickness of the inlet manifold flange is the same as the thickness of the new tubular manifold? Very often they differ and that can lead to inlet leaks.

[CityCharlie]

Is it possible that his dashpot damper is somehow faulty itself?

It certainly sounds like a fuelling issue somewhere along the line. I can assume your float level is correct?

[dklawson]

If you had to lower the jet by 12 additional flats just to get it to idle, I would be first looking at the supply INTO the float bowl. If the float bowl level is low you will be able to make the engine idle by lowering the jet. Once you rule out the fuel supply and float level,check for vacuum leaks as suggested above.

Earlier a couple of us assumed your carb is an HS4. Rev the engine until it starts to stumble badly. Immediately switch off while the engine is under duress. Remove the lid from the float bowl and see how much fuel is in the bowl. Let us know what you find.

[80sMiniCity]

Merry Christmas all.

Well I tried what dklawson recommended and found that I had a sticky float valve. I changed it and still had the problem, but the bowl is now filled with gas. Even after changing the float valve it still needs 24+ flats to get it running.

It’s a HS4 with a stock cam. The only things that were changed were the needle (aaa), intake (1.75” diameter), RC40 exhaust and a K&N air filter. The HS4 spacer is tapered from a 1.5” (carb side) to a 1.75” (intake side). I guess I wanted a smooth flow into the manifold. The gasket on the manifold is a HIF6 so the air doesn’t hit the gasket entering the manifold.

I took a video of the problem.

 BadHS4.wmv   1.84MB   28 downloads

[indymini]

I also have a 998 with stage 1 and am using an aau needle which came with the Stage 1. I don't know if that could make any difference but thought I'd throw it into the discussion. I recently changed to a 12g295 head and at that time changed to aaa needle. Runs great.
By the way I have an HS4 which was recently switched from waxtat.

Edited by indymini, 26 December 2012 - 09:00 PM.

[KernowCooper]

with the jet wound down so far you dont have a major air leak do you, if it will idle get some easy start and spray around the inlet to cyl head and if if revs up theres your leak ?

[Shifty]

Just listened to the video and it sounds like the timing is retarded.

I think you're barking up the wrong tree with the carb, try rotating the dizzy clockwise until the revs start to increase.

[80sMiniCity]

I checked the advance and getting around 25 degrees at idle and it drops as the engine revs. No problem there. I put back the waxstat jet and now it idles better and will rev without bogging down. Not sure why the fixed jet is not working correctly. I got it from a place in the UK that everyone knows along with the linkage conversion kit (BFS701SUL). Maybe the fixed jet needs a fixed needle? With the waxstat back in, 12 flats and it idles. Strange.

[Shifty]

I still think it sounded retarded, have you tried setting it by ear and ignoring the timing light?

- Start engine and run till warm
-Slacken dizzy and set engine to fast idle
- Rotate dizzy till you get the fastest engine note.
- Tighten dizzy and take for a spin.

If the car pinks then rotate the dizzy slighty anticlockwise and try again, repeat until no pinking/running on.

If the car feels sluggish then rotate the dizzy clockwise till it pinks and follow the above.

[80sMiniCity]

I’ll give it a try. One question. When I set the fast 1dle (1500rpm), should I lead the vacuum advance connected to the dizzy before I start to rotate the dizzy?

[Shifty]

Leave it connected.

I usually, hold the throttle open with one hand and rotate the dizzy with other(who says men can't multi task!!)

One thing I missed was that if you try and restart the car once you've altered the timing and it hesitates then its also too advanced.

You'll soon see if it makes a difference though.