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New RS38's, what main jet to start?

  • Thread starter Thread starter gearhead13
  • Start date Start date
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gearhead13

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What size of main jet should I start with for my RS38's? I put in 140's, they had 152.5's when I got them, I dont know what kind of bike they were used on.
 
In your 1300+ cc engine?
Mikuni jet size of 145-155 would be a good starting point I would think.
Hopped-up 1100's (1168's, etc.) typically use 142.5's and up.

Eric







Of course, after no one else answered your question and I did, now the rest of the crew will correct me.
 
Installed the carbs today, runs ok for not being synced yet, one float leaked and the A/P wasnt working so I have the bowls soaking in carb cleaner. Some blockage in the A/P bowl passages. Hopefully get them reinstalled and synced tomorrow.
 
gearhead13 said:
Installed the carbs today, runs ok for not being synced yet, one float leaked and the A/P wasnt working so I have the bowls soaking in carb cleaner. Some blockage in the A/P bowl passages. Hopefully get them reinstalled and synced tomorrow.
Click to expand...
Your bike is going to be a madman
 
Got it together tonight and went for a ride, carbs are so out of sync, sounds like its cammed to the moon:o
Lots of jump, seeing about 12-13 A/F at cruise but 14-15 when I give it throttle so tomorrow I'm going to raise the needles 2 notches and sync it.
I didn't want to wind it out because of the lean a/f.
And YAY, looks like all my oil leaks are fixed, although I won't know for sure until tomorrow.
 
Started with 150's went to 140's and now 135's and it still splutters under full throttle. a/p almost completely disabled. Seeing below 10 a/f under full throttle. I set the floats to 17mm, maybe a touch under 17. I guess I will try some 130's:confused:
 
gearhead13 said:
Started with 150's went to 140's and now 135's and it still splutters under full throttle. a/p almost completely disabled. Seeing below 10 a/f under full throttle. I set the floats to 17mm, maybe a touch under 17. I guess I will try some 130's:confused:
Click to expand...
Could the pump be too rich?
 
chef1366 said:
Could the pump be too rich?
Click to expand...
The pump is disabled:confused:
I put the 130's in it tonight and I am going for a ride tomorrow. They better work, cause those are the smallest mains I have:o I might take them apart and recheck my float level, set it at 18 mm maybe.
 
Silly question , but do you have a dual outlet fuel tap?

My 1166 was starving at full throttle on my kat, so I tapped and threaded in a 3/16" hose tail opposite the existing one which is easy on the katana taps and whallah!, a dual flow tap , no more fuel starving, and fixed the lean breakdown at full throttle. If you look at the front of the tap opposite the existing outlet you'll see a perfect location which lines up on prime and shuts off when the tap is off. I'll post some pics hopefully this weekend if I get a chance.

Or fit a Pingel dual flow tap.
 
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Spot1000Kat said:
Silly question , but do you have a dual outlet fuel tap?

My 1166 was starving at full throttle on my kat, so I tapped and threaded in a 3/16" hose tail opposite the existing one which is easy on the katana taps and whallah!, a dual flow tap , no more fuel starving, and fixed the lean breakdown at full throttle. If you look at the front of the tap opposite the existing outlet you'll see a perfect location which lines up on prime and shuts off when the tap is off. I'll post some pics hopefully this weekend if I get a chance.

Or fit a Pingel dual flow tap.
Click to expand...
Well, that could be. I am at a loss as to whats going on. I just have a T fitting on the stock petcock. When I turn it on prime all the fuel goes into one inlet, the T has to be exactly level for it to flow evenly. Maybe if I put the T up close to the petcock instead of down near the carbs. So, I would imagine that cylinders 3&4 would run out of fuel first. But doesnt explain the under 10-1 a/f ratio I am seeing. And it not like it runs wide open ok for a bit then stumbles, as soon as I open it up it, it splutters.
 
130 or 135 mains is what Mikuni calls for. They call for 140s in a full race prepped bike.
 
Oh yeah the pingel is a must if you don't have one already. I can't help much because I am using RS36s in my GS1100, but I did discover that the pilot jet seemed to be more critical than the main jet for regular riding. Obviously both have to be right, but for getting my bike running well for around the town stuff I could use various values of main, but only one size of pilot would work.
 
With my GS1100ED 36mm CV and 0.340 lift cams I would get fuel starvation issues in 5th gear with a stock petcock.

After the 1166, and head work it happened much quicker.

I now have a pingle single tap and don't have anymore starvation problems.

I was wondering if you believe the AFR reading from you meter. AFR 10 is pretty darn rich and you should be seeing soot on the plugs.
 
I have been thinking of getting a pingel for a while now, do I have to have a dual outlet or can I use my T fitting?
The a/f is in question because I ran the bike for a while with it unpowered. I recalibrated it but I dont know what effect running it unpowered would have. The plugs look fine, it runs ~13-1 at cruise and 13-14 under 1/2 throttle. 99.9% of the time I am at part throttle.
With the 130's its closer but still not right, I am thinking of pulling the carbs and rechecking my float level.
 
Make sure float height is where it's supposed to be so you're not chasing you tail on jetting. 17mm regardless of what size carbs you have.

I'm running a single outlet Pingel and granted mine is just a 700 but it never starves for fuel.
 
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