missfire / firing cyl 1 please help

[leeham]

Hi all

i have 1985 GSX 750 e 15000klms has been running great
heres the symptoms
at idle cyl 1 is not firing has (cold exhaust) good spark when checked
at 4k revs seems to fire a bit better, not great running but
run well with choke out and 4 k rev up (not perfect but)
i did replace plugs and oil last week and took of tank to do this.

i Have been running BP ultimate ULP 98 % octane (some here in australia tell me it's bad fuel but ?)

it seems like a carb problem, i have squirted a bit of carb cleaner in and around while running and motor off to check for air leaks outside and to "loosen slides" etc. the plug seemd a bit "lean"? as was a light tan colour compared to others balckish.

could it be stuck slide in carb?
crap in jets from removing tank (got shaken up a bit)
other carb issue, I will replace all rubber boots etc if those carbs come off!
other ideas please
as it is depressing me and i think it will have to go to the shop as i am not a carb man YET!!

i love the old girl and think i want to 7/11 it but thats another story

[flyingace]

I've found the easiest way to diagnose this is to remove all the plug caps then the spark plug from the non-firing cylinder. Turn the bike over - you should be able to see and smell the gas mixture coming out of that cylinder. If not, it probably is some kind of carb problem.

[rustybronco]

Hi all

"lean"? as was a light tan colour compared to others balckish.


as it is depressing me and i think it will have to go to the shop as i am not a carb man YET!!


i love the old girl and think i want to 7/11 it but thats another story

Light tan is correct blackish is too rich, is that with the choke on?

you will be!


7/11 ????????

[leeham]

tan plug (lean) was from after curing first plug problem, of fouled plug in 2

new plugs and then the missfire changed cylinders from 2 to 1.

pulled plugs and 1 was lean, yes choke may have been on as it ran better to get it home with choke on (kept revs higher)

misfire bad at idle, coldish exhaust not as bad at revs 4k

i checked there fuel in bowl but have not checked levels etc.

now more popping and farting form exhaust ?

7 /11 = 1100 motor in 750 frame

[tconroy]

tan plug (lean) was from after curing first plug problem, of fouled plug in 2

new plugs and then the missfire changed cylinders from 2 to 1.

pulled plugs and 1 was lean, yes choke may have been on as it ran better to get it home with choke on (kept revs higher)

misfire bad at idle, coldish exhaust not as bad at revs 4k

i checked there fuel in bowl but have not checked levels etc.

now more popping and farting form exhaust ?

7 /11 = 1100 motor in 750 frame

I would say you have a carb problem.Maybe time to take apart and clean.I know you probably didnt want to here that.Is your spark plug gap the same?

[Steve]

Sounds like a blocked passage in the idle or low-speed circuits of carb #1. Spray some carb cleaner in all the little holes you can see after you take out all the jets, then use some compressed air to make sure it's clean. Be sure to wear safety glasses as the spray tends to come out some rather unexpected places.

Not sure you need to be running such high octane. These bikes were designed to run on regular grade. If you have modified it to enhance performance it might require something more, but in stock form, the higher grade of gas just tends to build deposits on the valves and pistons that eventually REDUCE performance.

It is not the octane that provides the power. It is the higher compression in the engine. That higher compression heats the mixture more, which can ignite it before the spark. Higher octane is more heat resistant, so it waits for the spark.


.

[leeham]

yes remove the carbs

thanks for telling me what i dont want to hear :-D

i dropped it in to a bike shop and yes they think thats the issue.

so i am goint ot pull the carbs and clean them.

ive got that pdf from here for carbs and manuals etc so i hope i will be ok

you all can look forward to more questions!!