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Caspar
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Posted: Fri Oct 3rd, 2008 07:06 pm |
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I have fitted an air filter to my '48 ES2 and it's now running rich. Have lowered the needle (it's a pre- monoblock carb) but presumably I also need a smaller main jet. The question is how much smaller?
Any suggestions? Thanks.
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Frankfurt-Beesa
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Posted: Fri Oct 3rd, 2008 07:14 pm |
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| That is a 'try different ones until it's right' sort of thing, get the next three smaller sizes and try them out, remembering each time to try different needle positions. If you have a colotune kit it's quite a bit easier to get it spot on.
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Caspar
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Posted: Fri Oct 3rd, 2008 07:20 pm |
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Thanks for that.
I do have a colortune but have only used it on old cars at tickover to tune SU's.
What technique would you use to check a bike's main jet?
Thanks.
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Frankfurt-Beesa
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Posted: Fri Oct 3rd, 2008 07:43 pm |
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When I did my Beesa using colortune I followed the basic instructions. On a single carb bike it should be easier. Warm the engine, colortune plug in, check burn colour up through the revs, as long s it stays pale blue it's OK, as you should kow yellow is too rich and white too lean. It's not really different to doing it on a car.
It gets trickier with multi carb engines with balance pipes.
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Triton Thrasher
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Posted: Fri Oct 3rd, 2008 08:02 pm |
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If it runs well at full throttle and doesn't blacken a clean plug, don't change the jet. If it's "running heavily" as the makers used to say and sooting the plug, go down one size at a time until fixed.
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Frankfurt-Beesa
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Posted: Fri Oct 3rd, 2008 08:07 pm |
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Triton Thrasher wrote: If it runs well at full throttle and doesn't blacken a clean plug, don't change the jet. If it's "running heavily" as the makers used to say and sooting the plug, go down one size at a time until fixed.
'Swot I said, just with dff'rent words .
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Triton Thrasher
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Posted: Fri Oct 3rd, 2008 08:37 pm |
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Frankfurt-Beesa wrote: Triton Thrasher wrote: If it runs well at full throttle and doesn't blacken a clean plug, don't change the jet. If it's "running heavily" as the makers used to say and sooting the plug, go down one size at a time until fixed.
'Swot I said, just with dff'rent words.
Not exactly. You say Colortune, I say plug chop and feel how the bike goes.
You get different opinions on a forum like this.
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Frankfurt-Beesa
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Posted: Fri Oct 3rd, 2008 08:39 pm |
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Triton Thrasher wrote: Frankfurt-Beesa wrote: Triton Thrasher wrote: If it runs well at full throttle and doesn't blacken a clean plug, don't change the jet. If it's "running heavily" as the makers used to say and sooting the plug, go down one size at a time until fixed.
'Swot I said, just with dff'rent words.
Not exactly. You say Colortune, I say plug chop and feel how the bike goes.
You get different opinions on a forum like this.
True, but he's got a colortune, so could use it and get better result for the whole rev range.
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Triton Thrasher
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Posted: Fri Oct 3rd, 2008 08:44 pm |
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Frankfurt-Beesa wrote: Triton Thrasher wrote: Frankfurt-Beesa wrote: Triton Thrasher wrote: If it runs well at full throttle and doesn't blacken a clean plug, don't change the jet. If it's "running heavily" as the makers used to say and sooting the plug, go down one size at a time until fixed.
'Swot I said, just with dff'rent words.
Not exactly. You say Colortune, I say plug chop and feel how the bike goes.
You get different opinions on a forum like this.
True, but he's got a colortune, so could use it and get better result for the whole rev range.
I wouldn't use a Colortune under full power (because as a spark plug it is a bit crappy) and I wouldn't try to assess main jet mixture when the engine isn't pulling a load. You would. The chap hearing both opinions makes his own judgement.
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Frankfurt-Beesa
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Posted: Fri Oct 3rd, 2008 08:45 pm |
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Triton Thrasher wrote: Frankfurt-Beesa wrote: Triton Thrasher wrote: Frankfurt-Beesa wrote: Triton Thrasher wrote: If it runs well at full throttle and doesn't blacken a clean plug, don't change the jet. If it's "running heavily" as the makers used to say and sooting the plug, go down one size at a time until fixed.
'Swot I said, just with dff'rent words.
Not exactly. You say Colortune, I say plug chop and feel how the bike goes.
You get different opinions on a forum like this.
True, but he's got a colortune, so could use it and get better result for the whole rev range.
I wouldn't use a Colortune under full power (because as a spark plug it is a bit crappy) and I wouldn't try to assess main jet mixture when the engine isn't pulling a load. You would. The chap hearing both opinions makes his own judgement.
I agree.
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Triton Thrasher
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Posted: Fri Oct 3rd, 2008 09:31 pm |
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A slightly folkloric way to check main jet size, which does work on my Triumph is:
Fully warmed up, travel uphill at full throttle, at reasonable rpm. Suddenly reduce throttle opening to 7/8.
If the bike seems to pull harder, main jet is too small.
If it hesitates or splutters, then picks up, main jet is too big.
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