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adrianphu123

Rough idle on cold start after converter rebuild

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Hey guys,

 

I’ve got a bit of an issue after rebuilding the gas converter. Motor is a 250 crossflow running an Aussie B2 and Impco 200 mixer.

 

Had no issues starting but had to give 1/4 throttle to maintain idle when cold before converter rebuild.

 

After rebuild, car will start with 1/4 throttle but will run really rough until you start driving. Then it will cough a bit and then run and idle fine. Seems like the longer you leave it the longer it takes to cough and clear up and doesn’t do it at all on quick restarts ie. petrol station.

 

Converter has been rebuilt, lock off filter replaced and tested for leaks at converter and front lock off.

 

Anyone had a similar issue and can point me in the right direction?

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any chance there's a vacuum leak between the mixer(200) and the head?

i found this once, the seller of the car told me it had a burned valve as it was missing on one cyl(but when i did a compression test it was fine)

 

i assume it must have backfired once? blowing the gasket out.

otherwise look for loose carby bolts or vacuum trees or hoses off/cracked

 

if there's definitely no leaks, i'd consider just adjusting the mixture on the mixer until it smooths out. or get it on a analyser to be done properly.. how much LPG is it using per 100km, should be around 15L per 100km if reasonably stock engine.  if it's using more, it's probably too rich, if much less, probably lean

 

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Would running rich explain rough idle at startup and then clearing by up when hot? Is it possible that rebuilding the converter changed the tune? I’m getting about 24L/100km with city driving. Rest of the engine wasn’t touched, including the mixer.

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Would running rich explain rough idle at startup and then clearing by up when hot? Is it possible that rebuilding the converter changed the tune? I’m getting about 24L/100km with city driving. Rest of the engine wasn’t touched, including the mixer.
24L/100 is excessive, I would look at the converter secondary pressure being too high, or a holed diaphragm in the mixer which is causing a higher vacuum signal at the outlet and more gas to be drawn out.

In both gas cars I've had (Corty 250 with a straight gas CA300 and an EA with a dual fuel 200) I would get consistently 15L/100.

Something is wrong and it could have been multiple problems simultaneously before, and you've solved one but not all of them.

Sent from my CPH1920 using Tapatalk

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is the mixer a CA or FB one (label on the side) 

the FB (feed back) is designed to run rich and be "trimmed" by the impco commander computer thing using an O2 sensor etc.. if you have this, buy and fit a CA diaphram, i was told it should be simple as that? (never done it) 

otherwise, something's fucky.. either the mixture or power valve needs adjusting til you get it right.. (a ROUGH way i've been told is keep turning the power valve down (has L and R for lean/rich adjustment) until the car is gutless then gradually creep it up until you are averaging 15L per 100km ish with good power.. the other screw is base mixture that mostly affects idle but has some input to the overall mixture. 

 

i've never messed with them much, i've always just fitted another converter if that had an issue, and the mixers i don't think i've ever had an issue with. 

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Doesn’t have FB on it so I’m assuming it’s a clean air mixer. Did a test run after letting it sit for about 2 hours and it idled rough for about 3 minutes, felt a few slight coughs and then suddenly cleared up? I’ve got a gas tune booked in for Tuesday but the fact it clears up so suddenly is confusing. 

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next cold start you are going to do,  gently tip a kettle full of Hot(not boiling but hot) over the gas converter (take 60 seconds) then try start it after that, if it runs as warm. it's got to be GUNK in the hinges or the seats inside. 

 

a brand new B2 was about $180 ish last i heard(few yrs ago) so might be worth just getting a new one. i'm sure the gas tuner if they know what they are doing would spot an issue fairly easily with 25L per 100km its' a lot of gas(My 351 was using 20Lper 100 in XD and XE)

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