Thread: Carburetor Icing on Matrix !!!
08-11-2011, 12:59 AM #1
Carburetor Icing on Matrix !!!
Has anybody ever experienced the carbs icing up on thier ski ?
Last weekend I competed in a 100 mile endurance race on a lake. About half way through the race after I had been holding WOT for about 20 mins 7350 RPM a couple of things happened and I'm unsure what the cause is.
I hit a bit of rough water and noticed the RPM's hitting 7900 a couple of times as it unhooked then the ski seemed to lose power and came back to 6500 RPM WOT.
Thinking it was seizing I got of the gas but it came back to ilde !!! So I pulled the seat to have a look. I put my hand on the cylinders to see if any were over temp but they were all fairly cold then I noticed the carbs had a lot of condensation on them and were very cold.
I put the seat back on and took off again, it ran a little rough and then all of a sudden it was back at 7350 RPM and all seemed good.
I completed another 1 hr of WOT racing and no more problems.
The air temp on the day was 10 C / 50 F and the water is a glacier feed lake so cold, the lake is a 1200ft.
I'm thinking it could be one of three things I can think off.
1. Carbs iced up
2. Vapor lock in the carbs (don't really know what this is though)
3. I hit some sort of rev limiter that pulled the rpm's back. (not sure if the Matrixs had this type of set up)
4. Something more sinister ????
I would have thought if any of the problems were fuel stavation related it would have siezed. I pulled the plugs that night and had I looked at the bores with a borescope and all looks fine.
Fuel for the day was 98 ron octane. (here in N.Z we have three pump fuels 91, 95, 98. the 98 is only sold at a few places)
Thoughts on this would be good, if something is going on I would like to track it down.
08-11-2011, 07:36 PM #2
- Join Date
- Apr 2010
- Stamford CT
Don't know much about this engine. Does it run a thermostat or flow restricter of any kind in the cooling circuit? "Glacier feed" has got to be some pretty cold water. W/o a thermostat I would imagine the engine is operating at quite a low temperature.
08-12-2011, 12:07 AM #3
No thermostat or restrictor, standard Matrix setup. Wonder if I should look at putting one in ???
08-12-2011, 12:23 PM #4
It wouldn't be carb icing. I ride snowmobiles in the winter time and carb icing isn't a problem on the sleds in 30* below unless maybe there is water in the fuel. Sleds have wide open vents that let the cold air directly into the engine compartment too. The condensation on the carbs may have been from the cooler gas running through them and the heat inside the engine compartment coming into contact with the cooler carbs. Hard to diagnose without actually being there to experience it.
08-12-2011, 01:12 PM #5
Do the fuels have Ethanol in them? That could be an issue with the temperatures maybe.
08-12-2011, 04:07 PM #6
08-12-2011, 10:31 PM #7
50 degree air rushing into the hull would bring moisture with it.the air rushing thru the carb throats could cause the carb bodies to cool enough to start condensation to form on the outsides.
08-13-2011, 01:26 AM #8
If we rule out carb icing what else could it be.
I thought maybe a bearing in the jet unit might have seized but it came back to idle if it had killed a 1000rpm @ wot. I don't think it would have idled but instead stalled. I'm going to pull the unit to check but I don't think thats the problem. I will also check the through bearing. It might have run a bearing and then spun them in the housing or on the shaft.
Do these engines have a hard rev limiter? If it came unhooked @ WOT and the rpm's go high what happens.
What about the soft limiter ? Did the Matrix setup retain any sort of limp mode.
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