Help Find A Cure for Crazcnuk's bike?

[Crazcnuk]

I've done compression tests, 120-125 for all 4 at 3500ft.

I checked the diaphragms, at first it would take betwen 8 and 12 seconds for 3 of them to drop, the other would, more or less hang, there until you let your finger off the hole. I used some Lubriplate to help them seal, and now they will all stay there until you release them. (they are coming down, but VERY slowly).

My problem is top end. There is virtually none. My bike runs out of power in 4th and 5th gear at around 6500rpm.

Mid range is good, low range is now a bit boggy, it feels like I am starting in 2nd gear. When I lower the needles one notch, the bog goes away.

I've tried 110's (stock), 115's and 120s. All had the same top end problem. The 115s seemed to run ok, but the 120's were very rich in the mid range. At the time I had #45 pilot jets. Now I have the stock 42.5's.

[Hawkins]

do your plugs show a lean condition at WOT?

is there anything blocking the air inlet for the diaphragms? I remember posts from a few years ago about certain pod filters blocking air inlets on the carb inlet horn.

vacuum advance hose connected to the right place?

is the crank vent hose blocked? not sure if it would cause the symptoms you describe though, and I've had one too many tonight to think too hard about anything! maybe with slight leakage past your rings, the crankcase is getting pressurized at high revs, which could perhaps cause a vacuum imbalance and prevent the slides from opening any more??? Didn't some XS models have carbs with crank vent hoses connected to them?

[egsols]

Didn't some XS models have carbs with crank vent hoses connected to them?

Generally the crankcase vent runs to a nipple in the centre of the stock air box. When running pods the hose has to be rerouted with a filter installed in the end of the hose.

I have seen issues with clogged crankcase vents in the past causing poor running near top end due to the high pressure building up in the case. When the motor slows down some of the pressure releases allowing it to run somewhat better but at the higher revs it is fighting with itself too much.

[Crazcnuk]

I think he means the carb vents that run to the airbox. Mine is an 80, it doesn't have those vents.

I haven't done any plug reading lately. I almost wrecked 2 spark plug holes last time I did a chop test.

I am using stock airbox, no blocking of the vents.

Centrifugal and Vacuum advances both checked for function and hook up.

I haven't checked the crankcase vent, as I keep forgetting when I have the tank/carbs off. However, I am not getting any other blocked vent sypmtoms, ie, pressurized crancase hisses or leaks.

Since putting the needles in the stock spot (middle) My mileage has dropped from 41-43 to 38-39mpg.

I would really like to be able to video the carb slides in action to see what they are doing at WOT.

[Rasputin]

Didn't TC do a video of what happens to the slides under different loads on here? If he did not someone else did for sure. i think it was a youtube thing sorta. Maybe that would help you understand what yours are doing. If I find it in the next couple minutes I will add it here.

[Rasputin]

Try these

http://www.youtube.com/watch?v=tR63vrfhwr8&NR=1

http://www.youtube.com/watch?v=sMKGM...eature=related

[Crazcnuk]

Interesting, but I meant to see what MY slides are doing!

Since my problem is all at 7000rpm and up, I assume that my problem, if carb related, is all in the mains, and since I have tried mains right up to 120 with little or no change, the only thing I can think of is either I have a leak in the diaphragm system somewhere or a blockage in one of the main air jets.

Being able to watch the slides under load would show if one or more of the slides was 'lazy' or hanging up.

I am going to revisit my fuel lines and filters as well. I did not have this high end bog when my fuel economy was terrible...

[Crazcnuk]

Just thought of another possible thing to check.

I put snowmobile inline fuel filters on, to catch the Martian soil coming out of the tank, and then ran the lines to opposite sides, as others have done here.

I was not suspecting fuel starvation because the bike does not surge, or buck as most will do when running out of fuel.

However, is it possible that my fuel flow is slowed just enough that my float levels may drop a couple of mm under full throttle operation?

I would think this would give lean symptoms, a smooth lack of power, and yet not show up at lower gears because the engine flys by the rpms too fast?

[egsols]

However, is it possible that my fuel flow is slowed just enough that my float levels may drop a couple of mm under full throttle operation?

I doubt it but anything is possible. It's easy to check, just go for a run without them and see.

I've got inline filters and also the seats I put in are 1.40 instead of the 2.0 called for and I haven't found a problem with at WOT, however, I haven't been able to test in the upper gears.

No areas around here to really test out its full potential. Ontario has that great street racing law where anybody doing 50km/h over the posted limited is automatically labelled a streat racer and has their vehicle immediately impounded.

[Crazcnuk]

It's frowned upon, big time, here too. Hence the trouble with doing chop tests.

However, I do have a couple of stretches of rarely patrolled highway not too far out of town.

[petejw]

Hi Craz,
imho i wouldnt b lubricating the slides,
keep them very clean, any lube will cause
friction and prevent the slides from working
correctly, if viewing the slides from the air filter
side do they all sit evenly, out of the 4 i had only
1 sit correctly the other 3 were all slightly raised at
different heights, made a huge difference when corrected.

[Crazcnuk]

How did you 'correct' them? Mine all appear to sit the same.

But then that is the problem, everything seems to be as it should be, yet something is wrong.

[petejw]

i cleaned the slide bores of the carbies
with cleaner and polish til they all sat
evenly, mine were sticking at the base.
Ive read ur posts i cant think of y u wouldnt
b getting to redline.
Are u able to get to redline in the lower gears?

[Crazcnuk]

Yes, up to 3rd it hits 8500 no problem, but in 4th it slows right down at 6500+. It will still climb but slowly.

In 5th at anything above 7000 it will not accelerate, it just stays where it is until I hit a hill, where it slows down if I am going up, or speeds up on the downhill.

[petejw]

craz, when in the lower gears can
u actually hear the slides open fully at full throttle above 5000rpm,
when mine opens up i nearly go deaf by the roar. lol :-)
sounds like u mite b lean?
how does it run when its colder compared to when its full warmed up?
at this stage what have you done
to get the best result so far?
stick with it matey i know how frustrating they can be.