mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 18, 2019 11:53:00 GMT -5
Hey guys! So now with my 47mm big block running, during my commute today i had some weird stutter or hesitation while at or near WOT. Rpms were in the range of 74-7800, and was a really short "Blaagh" sound with power loss. Dropped the throttle and eased it back to WOT and was fine. Happened maybe 3 times in a 5 1/2 mile trip. Route takes me on 2 stretches, with some traffic and stopping in between.
Running a 90 main with a 33 pilot. Middle needle, didn't seem to like other needle settings. Stock air box and ext. Sea level in FL.
Can this been a symptom of a lean condition? It was chilly with 53F this am. Brand new iridium spark and fresh oil change. Entire bike has only 1009 km since August.
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Post by GrumpyUnk on Nov 18, 2019 12:09:41 GMT -5
Did it feel as if it was running out of gas? If you have a partially plugged fuel filter it can compromise the fuel flow. A picky vacuum petcock can also affect fuel flow. If it felt more like a 'bog' due to too much fuel, where opening the throttle more did nothing, but backing down to a lower flow seemed to help make the engine run better, it could be a too-rich condition at/near WOT. Flowing more fuel than needed can cause the engine to run worse at WOT, and improve at lower rpms where fuel flow is not at its max. Someone 'tuned' the main jet on one machine, such that it was VERY easy to see through the jet. As it approached higher rpm, it seemed to lose power and became unwilling to rev higher. I *think* it was too rich, and having a spare carb, I swapped them. It ran better, and actually had more power with a smaller main jet installed. tom
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mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 18, 2019 15:04:24 GMT -5
Did it feel as if it was running out of gas? If you have a partially plugged fuel filter it can compromise the fuel flow. A picky vacuum petcock can also affect fuel flow. If it felt more like a 'bog' due to too much fuel, where opening the throttle more did nothing, but backing down to a lower flow seemed to help make the engine run better, it could be a too-rich condition at/near WOT. Flowing more fuel than needed can cause the engine to run worse at WOT, and improve at lower rpms where fuel flow is not at its max. Someone 'tuned' the main jet on one machine, such that it was VERY easy to see through the jet. As it approached higher rpm, it seemed to lose power and became unwilling to rev higher. I *think* it was too rich, and having a spare carb, I swapped them. It ran better, and actually had more power with a smaller main jet installed. tom It was a blurp, quick in duration and went back to normal (whatever that means lol) running. It happens towards Wot and at wot. I guess that makes sense because at that point it's fully on the main jet. I have a 88 from what's left of my jet kit, I'll try and slap that in and see how it does. If it's more peppy and no more bog that it was for sure overjetted. How common is a 88 mj in a 47mm BBK? (Stock air) Edit: just rode it home and it did it several time especially past 30 mph, it would start to walk it's speed up then bog and lose power. I also noticed that reducing the throttle rapidly would cause it as well. I've seen another lost about this but can't remember what the cause and solution was. Def. Some kind of fuel issue.
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Post by scooterted on Nov 18, 2019 18:26:45 GMT -5
I used an 88 mj. With that setup.
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Post by tortoise2 on Nov 18, 2019 18:37:58 GMT -5
Def. Some kind of fuel issue. Not always . . example.
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mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 18, 2019 22:05:59 GMT -5
I used an 88 mj. With that setup. Since we share the same setup and if you sea level like me that might be what to doctor ordered. Thanks Ted. That adjustable cdi sounds super interesting. It's not very expensive, of course we have all heard about the cdi limitations on some stock cdi's. My bike is a 2019 Boom "gator", quite possible I'm hitting a rev limiter but i was able to get up to 35-39 stock and i never had that weird bogging/jumling before, and the throttle roll back bogging makes me think I'm over jetted. Thanks. I'll rejet on Wednesday, I'm stuck riding it as is until then, bit of it just overjetted i should be fine, just annoyed.
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Post by GrumpyUnk on Nov 19, 2019 11:31:13 GMT -5
I would have thought the jets installed would work fine. A 'blurp' to me might just be a cantankerous CDI or coil. Either could cause the spark to fail, causing a 'burp'. If you have a non-stock CDI, I'd suggest going back to normal, factory parts. Spark plugs and ignition systems can misfire under heavy load conditions, such as hill climbing. Could be the gap, the fuel:air mixture, weak coil, poor coil power/ground, the plug wire, etc. If the thing would start to slow down, with no apparent effect from opening/closing the throttle, I'd suspect fuel & carburetion. A short-term misfire generally points to ignition in my experience. tom
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Post by scooterted on Nov 19, 2019 13:23:24 GMT -5
I used an 88 mj. With that setup. Since we share the same setup and if you sea level like me that might be what to doctor ordered. Thanks Ted. That adjustable cdi sounds super interesting. It's not very expensive, of course we have all heard about the cdi limitations on some stock cdi's. My bike is a 2019 Boom "gator", quite possible I'm hitting a rev limiter but i was able to get up to 35-39 stock and i never had that weird bogging/jumling before, and the throttle roll back bogging makes me think I'm over jetted. Thanks. I'll rejet on Wednesday, I'm stuck riding it as is until then, bit of it just overjetted i should be fine, just annoyed. I am around 300-400 ft above sea level.
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mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 19, 2019 14:14:03 GMT -5
I would have thought the jets installed would work fine. A 'blurp' to me might just bebe a cantankerous CDI or coil. Either could cause the spark to fail, causing a 'burp'. If you have a non-stock CDI, I'd suggest going back to normal, factory parts. Spark plugs and ignition systems can misfire under heavy load conditions, such as hill climbing. Could be the gap, the fuel:air mixture, weak coil, poor coil power/ground, the plug wire, etc. If the thing would start to slow down, with no apparent effect from opening/closing the throttle, I'd suspect fuel & carburetion. A short-term misfire generally points to ignition in my experience. tom Yeah it only happens at higher rpm's, it's running a stock cdi that fairly new, the scoot only has around 1010km on it. Before big block it ran flawless. The WOT blurps only happen once the scopt starts to get up to speed, past 30 mph, the rpm range usually remains in the mid to high 7000s, only going to 8000 or slightly over that towards higher speed. Being a 47mm kit i wouldnt expect it to be so out of range in jetting, but i have had a lot of issues. There is also i think once or twice it might have backfired on rolling off the throttle, so is that a lean condition? It idles and runs up to around 60-70 percent, then will start to act up. Should I try a cdi change? Can you recommend one?
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Post by GrumpyUnk on Nov 20, 2019 10:00:50 GMT -5
Cheap things to try are the spark plug(higher compression with a larger cylinder/piston) as they can break down and misfire under higher compression. A coil doesn't cost much, and you'd have new plug wire & connector, but yours should be pretty new with 1k/k on the clock. Check the spark gap and inspect for evidence of running rich or lean. I would also check the CVT for belt condition. If you have a tach installed, note what the engine does when you go WOT while moving ~15-20mph(24-32kph). The rpms should not zoom to the 8k range, but should start to increase in tune with the speed you travel. IOW, if the rpms jump too high quickly, I think you are having slippage, guiding me to take a look at the belt condition. (shiny belt sides indicate slippage, I think) You could try backing off from WOT, just a bit, say 1/8th of the throttle and see if that makes a difference. I figure by now you have drained the carb float bowl into a container to look for water 'pearls' at the bottom. It's possible you may have a little H2O from condensation, rain, etc, which would cause 'blurts' of misfire. Wish the engine ran on water, but it doesn't. It will tend to clean the combustion chamber if ingested slowly without misfire. (Old mechanics used to trickle water into the intake with an engine running a good, strong, fast idle. Water flashed to steam, and helpd clean carbon deposits. It really does work) tom
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mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 20, 2019 16:13:29 GMT -5
Pulled the plug right after my run home now I'm new to this but this plug looks SUPER lean. Going to throw the 94 I have on hand in. Ordered a new jet set, my 92 main jet wondered off.
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mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 20, 2019 16:43:14 GMT -5
Put a 94 main in, ran worse and less rpm's with more of the bogging. I'll try a 88 next just to see.
Edit: put in the 88 no more hesitation! I guess I was overjetted. I need continue to dial in the pilot, but at while traveling wot like I am 99% of the time I know I'm in the right direction.
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Post by jackrides on Nov 20, 2019 17:25:43 GMT -5
Another cause of WOT 'stall' is a partially blocked fuel tank vent. Fill up the tank. If you have a vacuum petcock, apply vacuum. Open the float bowl drain into a clean container (so you can reuse the fuel). Does it flow freely all the way down? No, there it is. Yes, sorry 'bout that.
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mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 20, 2019 17:48:08 GMT -5
Another cause of WOT 'stall' is a partially blocked fuel tank vent. Fill up the tank. If you have a vacuum petcock, apply vacuum. Open the float bowl drain into a clean container (so you can reuse the fuel). Does it flow freely all the way down? No, there it is. Yes, sorry 'bout that. That's great info. I took it on a few test runs and the wot surging/hesitation silliness went away. I got some needle tuning now to do this weekend. Middle and low range hesitation. I see why these are so hard to tune, you have to make changes, ride and then see what works best. EDIT: I spoke too soon. As soon as I got the bike up to 35 and 7700-7800 rpm's, it would cut out. As I have a bridge on my route, when I came over the top and started coasting down I took off the throttle. Starting cutting out a bunch. It sounds like a restricted CDI. I ordered this adjustable cdi from amazon www.amazon.com/dp/B07GLGJ16T/ref=cm_sw_r_cp_apa_i_e5Y1Db0YKBHB9The reviews seem pretty good. Its showing up sometime tomorrow, I will have to report back. Funny how you think it might be one thing and you end up on a wild goose chase.
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mikeh
Scoot Member
Posts: 59
Location: Bradenton, FL
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Post by mikeh on Nov 22, 2019 17:31:13 GMT -5
welp. I put in the new CDI, no real difference, it will rev past 8000 on stand, actually revved to about 9000 something. i guess the next thing to do is check the belt, see if its shiny on the side as grumpy suggested.
if anyone has any further ideas, that be great. im out of them.
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