STILL need some help with tuning!
- Thread starter yamanube
- Start date
- Location
- Saskatoon,SK
I have one of your old Powerbomb's, and what a PITA to get setup (my first powerbomb), probably the silver one you mentioned. Almost gave up on it, then 'click' it dialed in perfect and is flawless (thanks....now! haha). The jetting is written down at the cabin so my best memory was that it was really square like 135 main,130 pilot, and the smallest return jet I had was a 75.
Sorry Yam, you cant have it back!!!
Sorry Yam, you cant have it back!!!
I am STILL battling with a huge flatspot in the midrange. Just to eliminate jetting questions I swapped on an SBN 44 125p 150m 2.0ns with 80f spring and a stock flame arrestor. The ski still idles well still struggles to build RPMs through the midrange and still rips up top (if I unload the pump or just force it through the middle RPMs).
I am stumped now, could a bad CDI, stator or coil cause this? The plugs look good, nice and brown and the issue is 100% consistent (doesn't change with engine or air temp). I haven't had a chance to run it in freshwater yet and don't have a lot if money to just throw parts at it (spent most if my free $ on the OEM carb because I thought that would do it). I would appreciate any input.
I am stumped now, could a bad CDI, stator or coil cause this? The plugs look good, nice and brown and the issue is 100% consistent (doesn't change with engine or air temp). I haven't had a chance to run it in freshwater yet and don't have a lot if money to just throw parts at it (spent most if my free $ on the OEM carb because I thought that would do it). I would appreciate any input.
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Just to confirm how it's affecting your midrange...if you're idling and nail the throttle does it:
a) go all the way up to max rpms smoothly
b) pull hard for a split second and then kinda blubber halfway up the wave
c) only have a dead spot if you're cruising around in the midrange and then try to nail the throttle
a) go all the way up to max rpms smoothly
b) pull hard for a split second and then kinda blubber halfway up the wave
c) only have a dead spot if you're cruising around in the midrange and then try to nail the throttle
It seems to rev decent between idle and 1/4 throttle. Doesn't lean bog or shut off and doesn't really seem to blubber just builds RPMs slowly (hard to describe). Anywhere above 1/4 throttle, regardless of how quickly I pull the throttle, it just kind of drags through the midrange. This is with either carb setup, if I just keep in the throttle it will get to a certain RPM and eventually feel like it gets on the pipe and instantly take off. If I jump or unload the pipe it easily revs out and if I keep the RPMs up it will continue to pull hard when it hits the water. Sounds clean and crisp on the stand.
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I have not, I do not have a primer hooked up, not even sure if I have one around my garage. The plugs show no sign of lean mixture though, with the powerbomb the plugs looked very rich, with the SBN they are brown.
I made another thread asking but go no response but I (just this morning) noticed that I have resistor plug boots on my coil. Have been running with resistor plugs, I have read that this can be both good and bad so I have no idea if that is contributing to my issue or not.
I made another thread asking but go no response but I (just this morning) noticed that I have resistor plug boots on my coil. Have been running with resistor plugs, I have read that this can be both good and bad so I have no idea if that is contributing to my issue or not.
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That is why I thought I may be having an electrical issue and not a fuel/mixture issue as I had originally thought. Also because a Powerbomb carb running completely different jetting and popoff has identical symptoms to an SBN44 with (what should be) very close to ideal jetting.
My bad, I missed that.
In my experience, electrical issues don't materialize in a mid-range flat spot. They show up as missing, stumbling, misfires, and not getting up to top RPM.
Just my experience, of course.
Has that motor ever ran right? Is this a new issue, or something it's had since you owned it?
In my experience, electrical issues don't materialize in a mid-range flat spot. They show up as missing, stumbling, misfires, and not getting up to top RPM.
Just my experience, of course.
Has that motor ever ran right? Is this a new issue, or something it's had since you owned it?
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I feel like it was never 100% (what I thought was due to working on getting my powerbomb tuned in) but it does seem worse recently. I think being in a bit lighter REV hull and having a stock intake grate may have also helped it jump past the problem area where this pig with a deep scoop grate loads it up a bit more and aggregates the issue. The engine has maybe a dozen or two tanks of fuel through it since I put it together. Electronics look clean but where from an unknown source.
It does run smooth no missing or shaking, it won't ever lose RPMs if you stab the throttle just struggles to build them and hauls ass up top.
It does run smooth no missing or shaking, it won't ever lose RPMs if you stab the throttle just struggles to build them and hauls ass up top.
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Also I am running a 14/18 concord and as CarterB and I discussed the other day it is likely overpitched BUT I have run it on all my motor setups in the past 5 years, including a bone stock '06 superjet and they all seemed to push it very well.
It's possible that your porting is just crap and that is actually causing the problem. Although I'd exhaust all other avenues before ruling that and trying a different cylinder.
From my experience, when my engines hammer hard on the bottom and then die about 1/4 to half, it's been because the high speed circuit is so rich that the engine can't burn it all until it reaches the upper rpms. If I can keep it in the upper rpms, it would stay fine and the plugs would look good but the final solution was to lean out the top end. I've found the high speed circuit to be harder to tune than the low. A 150 main with a 2.0 N/S seems like a lot of fuel to me for an engine that is running a stock head. You've obviously been at this for a while, so it can't really hurt to try. I'd try a 145 main or at least try closing the screws on the 150 and see what happens. Regardless of which way you need to go, I think that your high speed circuit is the problem so messing with pop off, low jet, and N/S are only going to make the problem appear at a slightly different rpms range.
From my experience, when my engines hammer hard on the bottom and then die about 1/4 to half, it's been because the high speed circuit is so rich that the engine can't burn it all until it reaches the upper rpms. If I can keep it in the upper rpms, it would stay fine and the plugs would look good but the final solution was to lean out the top end. I've found the high speed circuit to be harder to tune than the low. A 150 main with a 2.0 N/S seems like a lot of fuel to me for an engine that is running a stock head. You've obviously been at this for a while, so it can't really hurt to try. I'd try a 145 main or at least try closing the screws on the 150 and see what happens. Regardless of which way you need to go, I think that your high speed circuit is the problem so messing with pop off, low jet, and N/S are only going to make the problem appear at a slightly different rpms range.
D-Roc
I forgot!
- Location
- Dirty River Rider
i think you should do what supertune told you to try some time ago, bump up the compression to 195-210 and run a TL with a good curve. this is how he said you need to run this frankenstien motor of yours. i have found my powerbombs to be so easy to tune as a single and duals, very forgiving.
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TL will not happen, I may try and bump the compression but probably not anytime soon. I also have found the powerbombs easy to tune (on all but this engine) and am now seeing that it was likely not an issue with the PB in the first place. It honestly ran slightly better with the PB than it does with the 44 (when it was out of the funk). This exact setup actually ran very well in my REV hull, (better when I was back in MN on the flatwater than it did in the surf) which makes me think it could be a pump load issue?
I ported the cylinder myself but it is nothing more than a copy of the sport port template enlarged slightly for the 84mm bore. I only worked on the exhaust port and only widened it.
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D-Roc
I forgot!
- Location
- Dirty River Rider
Are those 760 cylinders meant for a 62t twin carb case? and you are running them on a single 61x case with the PB carb. this and your current pump load will make for a very unique tuning of the carb for sure. propably one that now one has done exactly. i think the tl would very much help your throttle responce and maybe over come this tuning problem. I think you maybe need to try a different jetting spec. I have duals and my main jets are 127.5, pilot 150, 2.5 N/S with 18psi pop off.
D-Roc
I forgot!
- Location
- Dirty River Rider
what is your reduction nozzle diameter?