Intermittant hesitation, brief loss of power

[ermie571]

Good afternoon all.

right.
2.1DJ running a carb and superunleaded (which is costing a fortune so need to get this sorted double quick time!)

History - started becoming lumpy on LPG. Couldn't sort the LPG so suspected air leak at manifold gasket. Replaced. Still lumpy...so back to basics. Get it sorted on petrol
Symptons - depress pedal to set the choke and it will start on the button. It also seems to start at 1800 revs, then drop down as it should. Driving along, using the accelerator all good most of the time. Plenty of pick up, and I can get it to 70 with no hassle. However, come off the revs and just maintain a steady speed and you can feel it occassionally held back, quick press on the accelerator brings it back. Idle was very high at 1400. Running temp remains low on the guage, rarely getting much above the white block, unless sitting in traffic when it will go up (as expected)

So far
1. Checked for air leaks - none found
2. New leads and sparks, dissy cap and rotor arm. (improved it, but still not 100%)
3. Once above was done, reset the idle to just over 1000 once warm
so next = fuel delivery. Check all filters - the inline one and the one in the carb. What do I clean the conical one with please? Can I spray with carb cleaner or WD40?

Think the gas is something different - bunged up shut-off valve a possibility after talking to gasure. But want to get petrol smooth as well

Please could someone tell me if the carb could cause this....mixture / butterfly setting or if timing needs to be investigated. Done lots of reading....but haven't been able to find anything definitive!

Many thanks

Em
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[California Dreamin]

Vacuum advance unit?
Non original petrol filler cap?


Martin

[kevtherev]

yes I was wondering if this was vacuum related.
the distibutor diaphragm relies on vacuum, on gas it would affect timing.
On fuel it would weaken the mixture aswell

suck on the pipe to the advance unit...if you can do it constant then it's holed

[ermie571]

Thanks for the advice!

Petrol cap is genuine, and seals well.

Will try the pipe to the advance unit....

Em
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[ermie571]

stupid question alert....

I have a spare carb sitting on the work surface at home which I am going to "explore".

Does the carb have to be on the engine for the "suck test" to work??

(told you it was daft....)

Em
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[kevtherev]

no..

[California Dreamin]

Does the carb have to be on the engine for the "suck test" to work??

Not sure what you mean by 'Suck Test' but vacuum will only be produced with the carburettor fitted and the engine running.

And the suck test is something you would carry out to the vacuum advance unit on the side of the distributor...to see if the diaphram in the unit is intact and the lever is pulling around the base plate in the distributor.
Martin

[ermie571]

Martin - Kev said to suck on the pipe to the vaccum unit - if you can continue sucking its buggered!

Tried the spare one indoors...and no, I cannot keep sucking...so it would seem that one is ok.

Cheers Kev


Now just got to check the one on the van!

Em
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[California Dreamin]

Martin - Kev said to suck on the pipe to the vaccum unit - if you can continue sucking its buggered!

Tried the spare one indoors...and no, I cannot keep sucking...so it would seem that one is ok.

Cheers Kev


Now just got to check the one on the van!

Em
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Em...you have me confused....easy I know but you mention the carburettor in your post but we are talking about the ignition distributor, two different things.

Martin

[ermie571]

Martin ---- thanks! I have had a DOH moment...I thought we were talking about the vacuum unit on the carb not the one on the distributor...

Now I realise the vacuum operates the secondary choke...or something....

and you helpful chaps were on about the one on the distributor....

God I feel daft. its just that I started the thread with carb in mind....and carried on in that ilk!

sorry

Em
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[jamesandtheopenroad]

Did you sort it?

[California Dreamin]

Another couple of ideas Em,

Accelerator pump built into the carb not working as it should (this device acts to enrich the mixture when pulling away by injecting an EXTRA amount of fuel into the venturi) sometimes the pump diaphram splits so doesn't work at all or the spray is more like a dribble.
You can check this statically by looking down the venturi and quickly operating the throttle, you should see a nice even spray of fuel directed downwards for 1 - 2 seconds (don't over do it or you'll flood the engine.)

Ignition issues...dropping onto 3 cylinders and then back onto 4, possibly down to a plug or plug lead momentarily breaking down.

Ignition switch fault, can happen but would be a total loss of power then back again.

Fuel blockages, in the filter or the small conical gaurse filter in the carb fuel feed. Also things like water in the fuel...

Air filter blockage, where the air filter is so blocked the engine runs OK until you go up a hill or put your throttle down. The mixture effectively richens because the air flow is so restricted, causing the engine to hesitate and fuel smoke.

Air leaks on the inlet manifold side.....air being drawn in but not fuel...engine runs very lumpy.

Martin



Martin

[ermie571]

Thanks for the input folks!

its running much better, and is back on LPG thank goodness

Timing was slightly out....timed by ear and the look of the engine by someone who knows what they are listening and looking for.

Had the carb apart and found lots of dried petrol in it, which was probably being washed through and clogging a jet, then being pushed through properly on acceleration. Took jets and cleaned as well.

Bit of oil in the carb, and its breathing a bit heavy under load, but its not smokey on start up. Just had oil change, and level is nearer full than empty....so that may settle once the level reaches 2/3 or half, which is where it seems to like it.

Its a pleasure to drive again. Just got to book it back in at the gas to have it set up on the gas meter.

Em
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