Any EMPI HPMX gurus here ?

[MTT3107]

So, I have an issue with my bugs engine, which I believe to be carb related.

Engine is a 1835cc, all new parts built last year. Magnaspark ignition system, dual EMPI HPMX 40's.

Car was running fine, but then started to develop this issue :
Whenever I am driving along at a constant speed, and then want to accelerate, it will stumble, sometimes backfire, but then will start pulling normally.
Also happens when I start to pull off from a full stop, like at a traffic light.

Last week I pulled the carbs, took them apart.
Found nothing wrong, except one idle jet had some crud in it.

While I was at it, also pulled the plugs, all look the same, nice light brown color.
Measured compression, 125-130 psi on all cylinders.

Cleaned, reinstalled carbs, problem persists...

Any ideas ?

[Schepp]

Sounds like possibly your accelerator pump isn't adjusted properly. Have you investigated that yet?

[Brian_e]

If it was fine, and recently started the problem, then it sounds like more plugged idle jets. If you are using the thin chrome stamped steel air filter housings, those have a lot to do with it. They are really hard to get to seal the dirt out. I prefer the CB cast filter housings. They are ridged and don't flex when you tighten the top nuts down.

Brian
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[MTT3107]

No, have not messed with the accelerator pump adjustment, since it says in the installation and tuning instructions, that they are adjusted at the factory and should not be messed with.

Idle jets ?
Like I wrote, I had the carbs apart, and found one jet with some crud in it, cleaned them all..
But I will check them again.

Also, how would the air cleaners affect the fuel going through the idle jets ?
They could affect the idle air circuit, but I blew those out too when I had the carbs apart.

[Brian_e]

[mikedjames]

It could also be something like a loose wire shutting down the ignition as the engine twists as you accelerate.

But with idle jets, sometimes the disturbance caused by fiddling with the carburettor picks up more dirt, so you have to check again.

Also I think the comments about air cleaners are that some of the filter mounting assemblies do not seal well and let in dust and dirt.
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1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[MTT3107]

[liquidrush]

I had a very similar issue and it was a plugged idle jet on #3 cylinder. At least they're easy to get out and clean. Of course mine are in the open on a buggy frame.

[MTT3107]

I'll check the idle jets again..

[MTT3107]

So, it turned out to be another clogged idle jet..
Cleaned it, reinstalled everything.

Synced the carbs again, and adjusted the idle mixture.

Cas runs great now.

Next project will be to install "weber windows", so it will be easier to get to the idle jets, and to adjust idle mixture.

[DesertSasquatchXploration]

You don't need CB anything to make it work right build your own jet doctors and a vent tube extension. Its stupid simple use steel fuel line drill for a press fit done deal. For the vent extension JB steel stick