Mikuni jetting

H

hkraanen@xs4all.nl

Junior member
Hi all,

My Mikuni TMR's 36 came pre-jetted by Topham with 155 mains.
Since the bike always ran fine and average MPG went up some 30 % (from 28.2 to 36.5 USA), (from 33.9 to 43.8 Imp.), I always considered it near perfect.
However Paul seems to run 132.5, I know he is at >1000m altitude, whilst I am at sea level, but then he has a flowed head, 80mm pistons, I have tapered (36 to 32) spigots, 75 mm pistons, 10.5:1, 39.5 inlet valves, Axtell cams.
Has anyone a direction to start with for a 1000cc triple like mine. Red, what size do you normally run in the RS carbs?

Thanks, Hein

 
Hein, if you refer to Paul LeClair, I believe you are attempting a doubtful comparison.  Paul's bike has Mikuni RS model carburettors.  There may well be a significant difference in the way different Mikuni models flow.
 
Hein,
For the engine configuration that you describe and if I was fitting RS 36mm carbs I'd start at 17.5 pilots and 127.5 main jets

never seen a set of TMR's yet, I asked my Aussie Mikuni importer for a set but he said he does not import that model

HTH
Red

 
 
Run it up on a dyno and see what the exhaust gas analyzer says.
 
Thanks all for directions:

Lawrence, both RS and TMR are smoothbore flatside, main differences are: TMR has rollerbearing slides (less clatter) and detachable spigots (cilinder head side, so they may be custom made).
Red, thanks for those figures, I guess the RS are quite comparable on 'flowing' to the TMR, so I may start at trying 130. Will check for pilotjet sizes as well.
Hi Lothar, always thought you are the total perfectionist..... and now you want me to take a very subjective impression as ' if it runs good, keep it that way'?
I do understand what you mean, but since my AFR (Dynojet Wideband Commander) metering unit shows values from 13 (idle) to 11.5 (4000 rpm and up), I am sure the bike might run a little rich right now.
Reggie, yes I did several dyno runs as well, did indeed show AFR's little to rich (12.0), where 12.8-13.2 might be optimum.

Just ordered a new Bosch LSU4.2 O2 sensor, this will be the third one in 20.000km, they seem to be rather sensitve, (as well as rather expensive at ? 175.-) but I don't use grease, brakecleaner, or whatsoever stuff that might ruin them. Anybody any ideas?
Will let you know my final outcomes.

Hein
 
I've been through a few wideband sensors also, I think is is the rich running at startup that kills them. When used in a car they are already in an environment that has been optimised. They are known to be sensitive to overfueling and oil contamination (common in a freshly rebuilt engine), guess the way around it is to warm the engine first then fit the lambda probe. Also recomended that the probe is fitted into the side of the collector to help keep any condensated water out.


  Keith
 
On the sensors, make sure your using a sensor with a heater. Assuming your mounting the sensor in the collector, its too far from the head to be heated quickly enough to stay alive for long. I use one with a built in heater and have had no issues with it for years.

For jetting with my Executive and 36mm RS carbs I'm at 15 pilot, 122.5 main, and a 9DZH-5 needle (P4 needle jet). I'm a slight bit lean on the main jet so will be bringing that up 1 maybe 2 sizes. The motor is stock displacement with J&E high compression pistons, Axtell cams, and tapered inlets. My exhaust has a large bore collector with modified stock style mufflers. The mufflers have the Corsa mod of four added holes in the back plus an enlarged center outlet. I live at a bit over 5000' altitude (1,524 meters).
 
Hein5960 said:
Hi Lothar, always thought you are the total perfectionist..... and now you want me to take a very subjective impression as ' if it runs good, keep it that way'?
I do understand what you mean, but since my AFR (Dynojet Wideband Commander) metering unit shows values from 13 (idle) to 11.5 (4000 rpm and up), I am sure the bike might run a little rich right now.

Hein
Click to expand...

Hello Hein,

If the dyno was an acceleration type and not a braked one, these figures are under acceleration, which doesn't really tell you something. If they are from riding, make sure the acceleration pump doesn't spoil the figures.

Main jet shall be done at WOT in 5th gear. Hard to do on open roads. If she goes close to maximum RPM (say: 7.800 - 8.200 on a 180 and 8.700 to 9.000 on an 120 SFC), main is about right.

All I say is: if you start at one point, you need to be ver structured to get them right and not burn a valve...
 
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