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Misfire under load


bengaku

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Hi so here is my problem i have swapped out old engine for a reconditioned one .car starts and runs have been out on the motorway but when accelerated away the car seens to have a misfire once car is in third gear or forth its fine .while sitting in traffic slight fluctuation on the idle dropping from 900 rpm to 500rpm then back up other than that as i said it starts and drives.im thinking electrical?  But i know that i have new battery new plugs,leads the distributor and coil are unchanged. So if anyone can shed light on this and timming was done by guy who swapped out engine .thanks for looking regards Paul 

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if the idle is floating it would seem its  set a bit on a lean mixture 

riche it up and re try,    often miss under load is down to spark plug , the fact they are new is not a reason to ignor them,

do make sure the new plugs dont have an R in the sufix

Pete

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Not sure about make of plugs will have a lokk tomorrow was out today same bit of a misfire then once up in third or forth seems to settle down and go along nicely but will check plugs and see if mixture is lean should be able to tell from plugs thanks for all the advice will keep you updated

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Actuallywhen i got the car it had a single carb the twibs had been taken off as the guy thought it saved money but i got the twins when buying the car and swapped them over i was unaware there woukd be a diffirence or that much if a difference between them ? But i havent been driving for very long about 4 years so if it does make a difference maybe that is why the car has a slight misfire when pulling away 

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I had similar sounding symptoms on my GT6 (a "soft misfire" in the high gears and a sporadic fluctuation in the tickover) After changing practically every ignition component and endless fiddling with the carbs I eventually tracked the problem down to the ignition timing. When set "correctly" using the timing marks and a strobe the misfire happened. Using the tried and tested timing method of adjusting the distributor to give the fastest tickover and then backing it off a gnats (which gave way too much advance according to the timing marks) cured the problem.

This might not be your issue, but a quick check to see if advancing the distributor changes anything might be worth a try.

Wayne

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Will i know my mate who did the work in his garage used a timming gun and said it was spot on so that could be it i did buy electronic ignition but my mate didnt know hiw to fit it so i said to leave it and i would hsve a look later on as i just wanted car back on the road rather than sitting in his garage 

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Im not even sure if the carbs are HS2 or HS4 but all i no is they were swapped over from single carb also i thought you could run a 1500 with HS2 it just wouldnt give as much at the top end then again not everthing you read  on the Internet is always true

 

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Difficult to tell as the carbs are on the other side......

HS2 carbs have their fixing holes vertical, one above the other. HS4 have the mounting bolts angled at approx 45degrees.

You can run a 1500 on HS2s but needs to have the correct needles fitted and the 1300 ones won’t be correct. Not sure there was ever a factory 1500 with 2 x HS2 to get a quick idea of what the right needles would be.

Nick

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