260 Main Jets in a '74 MK II With 750 Peashooter Exhaust and RH10 Heads?

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Dan1950

Dan1950

1974 MK II Roadster
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Does that sound like a good main jet choice for that combination?
 
I ran them for years. Upped to 280 with corngas gives better WFO for extended periods.
 
Dan1950 said:
Does that sound like a good main jet choice for that combination?
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Yes. I have the same components to run.
Main jet is only important at wide open throttle , which I never do , to protect my life and the precious driver's licence. To dial in the components you talk of ... I finally settled on a size 3 slide and a needle at the top clip. Plug pulls and analysis visually for correct grey/brown colour on the tips helped achieve that.
 
Torontonian said:
Yes. I have the same components to run.
Main jet is only important at wide open throttle , which I never do , to protect my life and the precious driver's licence. To dial in the components you talk of ... I finally settled on a size 3 slide and a needle at the top clip. Plug pulls and analysis visually for correct grey/brown colour on the tips helped achieve that.
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I'm aware of how Amal carburetors work and plan to do plug reading when the bike goes back on the road in the spring. Metering rods are in the top notch. Just wondering if that was a good starting point.
 
Dan1950 said:
I'm aware of how Amal carburetors work and plan to do plug reading when the bike goes back on the road in the spring. Metering rods are in the top notch. Just wondering if that was a good starting point.
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Metering rods AKA needles right?

Depends what you mean by ’top notch’ Dan…

I presume you mean the circlip is in the top groove of the needle? Thats the weakest position. Doesn’t sound right for an engine using 260 mains IMHO.

I‘d start out in the middle groove.
 
I ran settings you used, same bike. Ran lean but ran well. Lifted the needle one notch for more fuel found little difference.
Now that we will be forced into E10 will have to keep a careful eye on things and start again with the plug readings. If you are in the hot weather zone then you will be more liable to trouble with lean mixture.
 
Dan1950 said:
I googled it. It also applied to steam locomotive days. "Weights Fully Out" as well as your meaning.

I always used WOT, "Wide Open Throttle"
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Dan1950 said:
I'm aware of how Amal carburetors work and plan to do plug reading when the bike goes back on the road in the spring. Metering rods are in the top notch. Just wondering if that was a good starting point.
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Unless you are burning Racing Gas, or can turn back time 50 years, plug coloring is no longer an effective tuning tool. Only shows when it's way-to-hell-and-gone too rich. Or oil sooted.
 
Fast Eddie said:
Metering rods AKA needles right?

Depends what you mean by ’top notch’ Dan…

I presume you mean the circlip is in the top groove of the needle? Thats the weakest position. Doesn’t sound right for an engine using 260 mains IMHO.

I‘d start out in the middle groove.
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Well it runs superbly at all throttle positions except it seems to fall off a bit at WOT when revs get above about 5000 RPM. Funny thing is the left pipe is bluing a bit more than the right yet the plug on the left is black while the the right has the proper brownish hue.
 
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adding to the conversation - on my 74 Mk2 - 260 main, 106 needle, middle groove, 3-1/2 slides, stock OE peashooters and RH10 head. seems to run good from idle to WOT, w/o issues, but then again, have nothing to compare it to, so take it FWIW. i believe everything is configured to original factory specs.
 
joe czech said:
adding to the conversation - on my 74 Mk2 - 260 main, 106 needle, middle groove, 3-1/2 slides, stock OE peashooters and RH10 head. seems to run good from idle to WOT, w/o issues, but then again, have nothing to compare it to, so take it FWIW. i believe everything is configured to original factory specs.
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Except, if your running pump-gas, the fuel changed.
 
concours said:
Except, if your running pump-gas, the fuel changed.
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not sure what you're driving at - 99% of the time, i'm running 89 octane, non-ethanol. again, seems to run OK. can't complain. one thing i might add, i tend to run my timing a degree or two toward the "retard" side. not sure if this would be a benefit when using todays lower octane fuels - ?????
 
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joe czech said:
not sure what you're driving at - 99% of the time, i'm running 89 octane, non-ethanol. again, seems to run OK. can't complain. one thing i might add, i tend to run my timing a degree or two toward the "retard" side. not sure if this would be a benefit when using todays lower octane fuels - ?????
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What I'm driving at, is there are many areas non-ethanol is not available. Carry on.
This was in TX, , not so in the Northeast
 
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To me ethanol or non ethanol isn't an issue unless there is a likelihood that I may have to let the bike sit for an extended period of time. The main drawback of E10 is the moisture adsorption.
 
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Dan1950 said:
Well it runs superbly at all throttle positions except it seems to fall off a bit at WOT when revs get above about 5000 RPM. Funny thing is the left pipe is bluing a bit more than the right yet the plug on the left is black while the the right has the proper brownish hue.
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Try running with both fuel taps open. I've had misfire at high throttle openings that was cured this way. I should pull the fuel taps out and check for dirt on the gauze but have been too lazy...
 
HoveToo said:
Try running with both fuel taps open. I've had misfire at high throttle openings that was cured this way. I should pull the fuel taps out and check for dirt on the gauze but have been too lazy...
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It doesn't misfire it just kind of wheezes like it can't quite breath. I will be able to get it sorted out once I get everything else copacetic. If anything it seems like it might be rich. The pipes are sooty.
 
Dan1950 said:
It doesn't misfire it just kind of wheezes like it can't quite breath. I will be able to get it sorted out once I get everything else copacetic. If anything it seems like it might be rich. The pipes are sooty.
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I agree with dealing with known maintenance items first. There may be 2 things going on. As you know, blue exhaust = hotter, which suggests lean. The soot deposits may be oil?
 
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