Engine trouble - thoughts?

[jason]

I've recently started driving my car after a 3 month break while I renewed the entire front suspension. Since getting it back on the road it's been suffering from some intermittent engine problems that I'm struggling to fix. I also pulled the tank out at the time of suspension and resealed inside of it. I can't see how it's related to the issue, but including this for context.

Here's what happens

The car starts, idles and drives completely perfectly until it gets up to temperature and I give the accelerator a little blast past 3500rpm with quick acceleration. Standard slow acceleration is fine. Shortly after that it dies like it's intermittently losing power. The engine dies and I pull off the road. It will restart and if I can manage to keep the revs above 2500 I can keep the engine running, but it splutters, coughs (no backfire) and generally wants to stop. When it happens I've checked lose ignition wiring etc, but cannot find anything. It kind of seems like a dirty fuel crossed with ignition problem. Without doing anything it eventually fixes itself and away I drive until next time.

Today I replaced rotor and distributor cap and it happened again after I took it for a drive. It has MSD, new coil and leads about 18 months ago and it's never given me a minutes trouble, all are relatively new.

The strange thing is that if I don't give it a little blast it drives fine. I also can't reproduce the problem with it at temperature and revving it while stopped.

I thought distributor advance might be sticking but can't think of a way to check timing on my own with car running. A basic check of distributor with cap off and twisting the shaft shows normal spring advance action.

It always comes right after about 5 minutes of 2500-3000 revs while stationary.

Thoughts?

[reedminor]

is the coil one of the new chrome (ie not black) brazilian / spanish Bosch coils?

I had one fail in under 2 years..... and the symptoms sound similar.

I have a Parts Klassik cdi - but have heard some stories about the msd ignition packs....

So its sounds like coil or cdi or a combination of the 2.

Justin

[klasikcis]

I am no expert but you have played with the fuel tank. Sounds like your fuel line or filter is partially blocked.
Nev

[PCM911T]

I agree with Nev, it sounds like a fuel blockage under load. Did you clean the tank? Did you change the in tank filter? Add new in line filters? Are we talking webers? There is an internal gauze filter in each weber. If the car runs and idles when not under load it doesn't sound electrical. Finally did you replace the rubber lines near the tank, the insides can collapse or rot and you did use new fuel didn't you.
Paul M

[epilot]

I agree with Nev, it sounds like a fuel blockage under load. Did you clean the tank? Did you change the in tank filter? Add new in line filters? Are we talking webers? There is an internal gauze filter in each weber. If the car runs and idles when not under load it doesn't sound electrical. Finally did you replace the rubber lines near the tank, the insides can collapse or rot and you did use new fuel didn't you.
Paul M

+2 I had similar symptoms after fiddling with the foam in the fuel cell of the racer, small in-line filter was partially blocked with bits of foam that i'd been fiddling with ...

[Fishcop]

I agree, likely a fuel issue. Pull your jets and carriers, blow them out with carb cleaner and compressed air. Before I resealed my tank I was doing this every 6 weeks...

[Merv]

As John says, pull and clean the jets. Add new inline filter also.

[jason]

When I resealed the tank I replaced all soft lines and changed the inline filter in engine bay. I soaked the tank filter in marine clean and it looked pretty good after. The carbs are Zeniths and completely rebuilt not long ago. The symptoms seem a little different than starving of fuel though. After it cuts out and I leave the ignition on and fuel pump therefore running - it does not easily start. As for dirty jets - I wouldn't expect these to come right without cleaning. However, the symptoms are more closely aligned to a dirty fuel type of indication than anything else - the only thing that makes me think it's not fuel is that it can be reproduced each time I'm in 2nd/3rd gear and give it some boot. I'll go through it all again tomorrow just to eliminate fuel system.

The other piece of info I forgot to mention was that after I manage to restart it and it's only just managing to run badly at higher revs is that the tach needle is bouncing up and down.

So, I'll eliminate fuel suspicions tomorrow and report back. I'm thinking Justin might be on the right track with coil or MSD though.

[SM911]

Bad spark plug leads can cause symptoms like this as well.

[jason]

is the coil one of the new chrome (ie not black) brazilian / spanish Bosch coils?

I had one fail in under 2 years..... and the symptoms sound similar.

I have a Parts Klassik cdi - but have heard some stories about the msd ignition packs....

So its sounds like coil or cdi or a combination of the 2.

Justin

Coil is an MSD blaster coil. It was the one recommended with MSD system. I'll google msd problems a little more too.

[Merv]

Jason there are a thousand threads like these and all can have different resolutions - electrical, fuel, timing and so on. I once found a piece of wheat stalk in a fuel line that meant that over 3.5k rpm the motor started to lean out and cut out. It seems that the main thing that has changed in your case is the tank cleaning and the first avenue would be a restricted fuel line, filter, sticking float or jet. You have replaced the rest so, jets are next to check. Also the float levels (critical for starting), fuel transition outputs on the Zeniths are key milestones. I have just sent several weeks getting my Zeniths right. Simple carbs, but they don't like dirt or gum.

If they are all good then the electrics and timing come into question.

[jason]

Bad spark plug leads can cause symptoms like this as well.

I forgot to mention that these were also replaced at the time of the MSD with pretty expensive ones too. I did a visual check and have reseated all a couple of times when it won't properly start and they didn't seem to make a difference.

[jason]

Jason there are a thousand threads like these and all can have different resolutions - electrical, fuel, timing and so on. I once found a piece of wheat stalk in a fuel line that meant that over 3.5k rpm the motor started to lean out and cut out. It seems that the main thing that has changed in your case is the tank cleaning and the first avenue would be a restricted fuel line, filter, sticking float or jet. You have replaced the rest so, jets are next to check. Also the float levels (critical for starting), fuel transition outputs on the Zeniths are key milestones. I have just sent several weeks getting my Zeniths right. Simple carbs, but they don't like dirt or gum.

If they are all good then the electrics and timing come into question.

Hey Merv, you're right about 1000s of threads! I think that's why I posted here - you guys are always very knowledgeable. Every one of the other threads has someone giving an opinion without necessarily having any knowledge. Too much noise.

I also spent ages getting my Zeniths right originally. They are definitely a good carb, but need to be 100%. I'll definitely open them up again and check tomorrow.

[chesterc]

somewhat similar problem with my car with 2.2 MFI turned out to be failing alternator with inconsistent charge. rebuild and its been good as gold
chris

[Merv]

Jason it is important to be systematic even though we all look for a quick result at times like this. When you open up the Zeniths, run the car first and then after switching off and cooling for a bit, measure the fuel level in the bowls with the tail of your Vernier gauge from the top edge. Not sure which Zeniths you have but the manual should tell you the measurement. On the 32's it should be 18.5-19mm.

Then check the jets (main, idle and idle/air jets) and clean them. If you don't have any pin gauges you can try to use some fishing line or similar to check the apertures to an extent. Air pressure is better. Have a look at the bottom of the bowls for sediment. Jim might chime in as he is an expert on carbs.