M95 CW tuning conundrum

[matt glascock]

Stock M95 CW set-up other than 2nd over-bore, PVL ignition, and mild port work, and . Hare scrambles. Air temp 74, RH 70%. Pre-race jet run plug chop looks like perfect jetting. About 20 minutes into first moto, the bike ran poorly in 1st and 2nd gears through all rev ranges. Once in 3rd gear and above, smooth delivery of power through all carburetion ranges, came on the pipe well, and revved smoothly and progressively up to about 8500 RPM according the the ear tach. This is a bike I usually race MX and so 1st and 2nd gears are rarely (almost never) used in lieu of keeping the revs up in 3rd with clutch fanning. This, however, was ran on a very tight woods course so the problem dogged me through the entire race. Plug looked great, but no jetting area at the track. Clutch rebuild after this season anyway, so I brutalized the clutch and did well. What I don't know for sure is has this issue been an issue for a while and I never noticed it until now. What would account for inconsistent performance in gears 1 and 2 and awesome performance on gears 3 through 5? Thanks guys.

[viclioce]

Watching..... Victor

[mac]

I’m also watching to see what the more knowledgeable say because this is a tough one (for me). The only thing that seems to be different is your mph are more in 3rd on up but I can’t see why that would matter. My first thought was ignition but I would think that would be an issue in any gear. Maybe some kind of drag on the motor or drive line that is overcome the faster the bike is moving ?
I’m very curious to see what it ends up being.

[matt glascock]

You and me both, brother!

[Bullfrog]

Saw your message shortly after returning home from City Council meeting. Read the message and thought, whaaaaaatttt?

Went off-line.

Came back to read the message again. Had the same thought, whaaaaaattt?

Will sleep on it.

Did mention, whaaaaattt?
Ed

[ossa95d]

Matt, the only thing I can think of is that in tight woods situations in first and second gear you are usually feathering the throttle, but once into third or higher in the more open sections you're back on the main jet. My thought is rich in the mid range but once on the main the condition clears. On an MX course you're almost always on the main jet.

[matt glascock]

Agreed Captain. This is a three-Whaaaattt situation. Thanks Pop. I will try raising the needle one notch and see if that cleans it up. I don't have any pilot jets in my kit here so that's about as much adjustability I have on this trip. I can assure you, my first move once I get home is a complete carb cleaning/overhaul then it's back to the drawing board.

[Dale]

A long shot, but what if the float level is putting a little too much fuel in play until you consume more at higher speeds? What ever the cause, it is a different symptom for sure!

Also check your choke lever. Is it tight? Anything in contact or could be coming in contact with it such as fuel line or wires?

[matt glascock]

Great suggestions Dale. I will for sure confirm proper float height when I dig into the carburetor. Nothing seems to be impacting the choke lever but the plunger will get a careful inspection.

[Bullfrog]

OK Matt, I think I'm ready to opine on your situation -- I'll try to keep it "under book length"

You gave me an inch (so I'm taking a mile) when you wondered if this running problem has been an issue all along . . . and you've just noticed it. I think you nailed it with that question. But let's get into the answers/recommendations.

1. Over simplifying ------ pre-race jet run, plug chops are main jet checks only. Doesn't tell you anything about pilot jet, slide or needle ranges (i.e. closed to 3/4 throttle). A reasonable thing to do with a machine which has proven to be jetted right at all throttle settings at home, but which is now being checked at a different elevation/humidity/temperature.
2. Again, over simplifying ------ "ran poorly in 1st/2nd at all rev ranges" -- I kind of don't care about "rev ranges". I want to know throttle settings. The engine can run from idle to 9,000 RPM at 1/8th throttle under the right situations (think highway cruise on a slight down hill or with a good tail wind). In a like manner, under the right conditions (let's say 1/2 throttle in third gear, the engine could probably pull nicely from 2,500 to 9,000)
3. Sticking with over-simplifying ------- the carb can't discern which gear you are in. So I'm guessing that you (the rider) were doing something different (probably throttle) in 1st and 2nd that you weren't doing in 3rd, 4th and 5th. I'm guessing there were a lot of throttle chops to zero in 1st and 2nd and that you seldom got below half throttle in 3rd-5th.
4. Starting to summarize and head toward recommendations now ------- I think the reporting of symptoms missed an important factor. The engine ran poorly when throttle work below half was being used . . . and much better above half throttle.
5. Recommendation: Find a place out in the country with a long stretch of little used gravel road. With a warmed up engine, do a gentle acceleration run in the following manner -- "short shift" at the minimum engine RPM which you think will "pull" the next gear till you get into 3rd, then slowly roll on the throttle while listening for burbles(rich) or clean running as the throttle is advanced. This test can also be done in 4th - the higher gear gives you more time at each throttle range to listen/feel for how happy the engine jetting is. Make mental notes of how the engine runs at every fractional throttle setting.
6. Going out on the limb now ------ I think you are going to find that you have some very rich situations going on in the bottom half of throttle settings (which you have never noticed before on the track).

My 2 cents. Hope it helps.
Ed

[matt glascock]

Excellent Captain! You've taken the time to develop a logical, systematic work-up. Much appreciated. Upon my return, a complete carb cleaning is in order. I will preserve the current settings so when I embark on the work-up you suggest, I will be starting where we left off. Funny how the bike seems so dialed for one racing discipline and so totally off for another. Truth be told, the bike has been set for MX exclusively until happenstance got it thrown into a woods race. Thanks again Captain. Always appreciated.

PS - opening a new jet thread and hoping you'll weigh in.