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Post by rusty on Apr 3, 2016 7:05:10 GMT
Hey guys got a bit of a mystery that I could do with a second or third opinions on... My bike has a slabbie 750 engine and carbs and ever since I've had it number 4 cylinder has, occasionally stopped firing...I finally got to the bottom of that issue and fixed it... Now however, number 2 doesn't want to fire even tho it did before... I've checked and changed the spark plugs, the coils work fine but I will probably get some from a newer bike just in case..I know that all the jets and needles are clean and clear and fuel is getting through...when I squirt into the carb while the engines running the idle drops and 9 out of 10 times it stalls  Any ideas...is it fuelling or electrical? |
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Post by paddy on Apr 3, 2016 7:32:54 GMT
Is it intermittent like it was on no4 or just wont fire at all? What was the issue with no4? I guess swapping your coils round would eliminate electrical if the issue doesn't move cylinders. If you switched the coils round then it would move to no1 or 4 as I can't remember which way you count from lol (it will move to the right end cylinder when sat on the bike)
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Post by bigkenxx on Apr 3, 2016 7:52:50 GMT
Also double check the carbs are clean , I know this is daft but crap can suddenly appear you could try to hold your hand on the back of the carb , also swop the plug around or try one that you know that is good in number 2 as new plugs are rubbish just because they are new doesn't mean they are good
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Post by bigkenxx on Apr 3, 2016 7:55:11 GMT
I have some spark testers which are a brilliant cheap bit of kit or get a inline one it rules alot of ignition problems out straight away they saved me hours of pissing about
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Post by paddy on Apr 3, 2016 7:57:11 GMT
Also double check the carbs are clean , I know this is daft but crap can suddenly appear Yea like the endless supply of excess jb weld blocking the pilot jet on no4 (or is it no1?) on mine lol. |
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Post by bigkenxx on Apr 3, 2016 7:58:52 GMT
Have you taken the float bowl off number while it's still mounted on the bike to see what's happening
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Post by paddy on Apr 3, 2016 10:15:05 GMT
It may have been said before? but I like that mixtures can/should be adjusted for individual cylinders rather than all the same. Didn't realise this but when thinking about it it makes sense.
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Post by paddy on Apr 3, 2016 10:41:21 GMT
I wish I had a decent long reach screw driver as mine is shit
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Post by bigkenxx on Apr 3, 2016 10:47:26 GMT
Get them on eBay
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Post by paddy on Apr 3, 2016 11:49:48 GMT
I did  |
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Post by bigkenxx on Apr 3, 2016 12:01:02 GMT
Oh lol
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Post by rusty on Apr 3, 2016 17:31:13 GMT
Is it intermittent like it was on no4 or just wont fire at all? What was the issue with no4? It doesn't fire at all The problem with number 4 was a fuelling issue...the jet needle was shaped like a banana but since changing it and cleaning it's been perfect |
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Post by rusty on Apr 3, 2016 17:33:15 GMT
Also double check the carbs are clean , I know this is daft but crap can suddenly appear you could try to hold your hand on the back of the carb , also swop the plug around or try one that you know that is good in number 2 as new plugs are rubbish just because they are new doesn't mean they are good Trying another plug..will give that a go tomorrow but it was running fine before...I've put my hand on the back of the carb and can feel it sacking air I will be cleaning the carbs again as I've taken the filter off so some crap may be to blame |
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Post by rusty on Apr 3, 2016 17:37:24 GMT
Coils are 1+4 & 2+3 so that suggests this issue isn't related to the previous one unless it was a fuel problem in the first place, however I could be a HT lead tracking out & that would cause a misfire but not always cause it to stall, swapping leads to see if it moves helps in finding a problem like this EG #2 to #3 & see what happens
I cant remember off the top of my head but does the slabby have 2 ignition pickups ? if so one of those could be at fault, this would normally cause problems on 2 cylinders, substitution is the best plan there
Finally & most likely imo is carbs as ken says it don't take much crap to mess up a previously mint set of carbs, a good gauge for how things are running (or not) is an infrared thermometer, point it at each downpipe & see if the temps are roughly the same, lastly & especially on the older stuff the mixture screw, most people will set all 4 x amount of turns out as per the book but this isn't always what the bike needs after 1000's of miles of wear/use/abuse & the vagaries of the original machining A twiddle in or out on the screw for a lazy cylinder will sometimes see it picking up straight away basically that's what is done with a gas analyser on the dyno EG put them where they need to be rather than what the book says
Hope it makes sense & helps a bit mate I've got spark testers and they all seem fine but I'm going to get some more coils soon just in case but it's odd how it's stopped all of a sudden Number 2 downpipe is cold enough that I can hold with my hand even when the bikes been running for 10 minutes All of the mixture screws need adjusting as the mixture is over rich so when I take the carbs off again I'll set them leaner |
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Post by rusty on Apr 3, 2016 17:37:57 GMT
Have you taken the float bowl off number while it's still mounted on the bike to see what's happening No |
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