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| Tuning help https://www.mudmotortalk.com/mmt_v2/viewtopic.php?f=3&t=71396 |
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| Author: | Heavyshot [ Tue Oct 10, 2017 7:26 pm ] |
| Post subject: | Tuning help |
Hey guys I have a 35cdi that I’ve put heads, cam, q exhaust, k&n, and cleaned up the intake manifold on. I had major speed/power gains after the cam/exhaust/manifold work went from 25mph to 30. I put the heads on last weekend and didn’t pickup anything noticeable but have noticed that it seems to be running richer than before from plug inspection. Currently has a 138/144 main in the stock carb and I was able to tune the off idle bog out again with the air screws 3 turns out. It will spin a baggy worked big blade at 4600 but it just won’t bust 30mph and it doesn’t feel like it pulls the same as before the heads. Is it normal to need to lean these out a little after above mods? I’m at around 1100ft elevation. Also wondering if I might should drop a tooth on the lower drive pulley? |
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| Author: | brycecheramie [ Tue Oct 10, 2017 7:41 pm ] |
| Post subject: | Re: Tuning help |
im not familiar with elevation. but I would think with those mods you would need a 160 main jet or so But like I said, im not sure how much the elevation makes a difference |
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| Author: | Will C [ Tue Oct 10, 2017 8:07 pm ] |
| Post subject: | Re: Tuning help |
Stock carb Bryce. I think your plugs looking darker is from a lot of idle fuel. I would bet your are lean. Also a real hungry motor can run out of enough air to keep up "stock carb"sooner than a milder motor. And yes if your running a stock carb gearing up some will keep motor in its happy place. "Let it pull vs trying to rev a stock carb real high" |
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| Author: | brycecheramie [ Tue Oct 10, 2017 8:44 pm ] |
| Post subject: | Re: Tuning help |
| Author: | Will C [ Tue Oct 10, 2017 9:43 pm ] |
| Post subject: | Re: Tuning help |
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| Author: | MaXXis85 [ Wed Oct 11, 2017 5:56 am ] |
| Post subject: | Re: Tuning help |
Stock Carb shouldn't have an issue spinning to 4600-4700. You can do a plug test and dial in your jetting with one Full turn of color on the base ring of the plug, DONT look at the porcelain. Just the thick ring of the plug that the ground strap is welded to. They will be Shiny and silver new, Warm motor up with original plugs, then swap the new gapped plugs in and go WOT for about 5 minutes then shut her off and coast to a stop. Pull the plugs and get a base line reading . If the plug isn't a full tuen of color you need more fuel. If its Heavy and sooty with a full turn its too rich, a light blackish or tan full turn of color is what you want. Also look at the ground strap to determine heat range, You want the color change line to be about halfway of the strap... Like in the bend to be about perfect. |
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| Author: | Heavyshot [ Wed Oct 11, 2017 3:47 pm ] |
| Post subject: | Re: Tuning help |
I appreciate the help guys. I've attached a few pictures of the plugs from a WOT run with no cool down time. Looks rich to me. How does one determine if it is too much fuel...or not enough air? I'n not against swapping to a Mikuni or a Lectron ultimately but I would like to be able to get by with the stocker for at least a little while. |
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| Author: | Will C [ Wed Oct 11, 2017 7:32 pm ] |
| Post subject: | Re: Tuning help |
By the book it looks ok. But that ring could still be from the 3 turns out idle fuel. The newer carbs run those little jets you mentioned. The older carbs were jetted fatter. Seems like your the kind of guy that likes to play with these. A wideband o2 sensor is a very fun toy and under 200bucks. Your spinning 4600 now and not getting 30 makes me think "trim down" or something else weird is going on |
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| Author: | CypressCritter [ Wed Oct 11, 2017 7:42 pm ] |
| Post subject: | Re: Tuning help |
Worked big blade at 4600 but it just won’t bust 30mph ???? sounds more like a boat or load problem, also possible maybe prop doesn't have enough surface area to get a good "push"! |
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| Author: | Heavyshot [ Wed Oct 11, 2017 8:05 pm ] |
| Post subject: | Re: Tuning help |
It’s on a 1748 Prodigy .125 that is setup super light pretty much just me 160lb.6 gallons of fuel and battery. I’ve got a borrowed 3 blade off a delta level 3 to try and access to a hand held wide band that I’ll get some numbers from and report back. I just figured it would run mid 30’s I can run it up to to the rev limiter and it pulls like hell trim back down to 43-4400... still 30. |
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| Author: | Heavyshot [ Wed Oct 11, 2017 8:11 pm ] |
| Post subject: | Re: Tuning help |
I did verify it’s geared at 38 top/50 bottom |
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| Author: | CypressCritter [ Wed Oct 11, 2017 8:18 pm ] |
| Post subject: | Re: Tuning help |
only time my boat gets faster than 32 is in little or no water on good mud then it hits 35-36(hammer prop). |
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| Author: | Russ [ Wed Oct 11, 2017 8:25 pm ] |
| Post subject: | Re: Tuning help |
Spinning a prop at 4600 rpms but not running any faster means you need more prop. At 4600 and damn near the same exact boat with a 48t gear (very close gear ratio to 38/50 30lb gearing), I run 35+ solo with tools and an 40qt ice chest full. I'm not trimmed up very high, either. Maybe a 4ish ft high rooster tail. #CFFITR #TheGhostBoat #whoneedsphysicsihaveamudmotor |
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| Author: | Will C [ Wed Oct 11, 2017 8:46 pm ] |
| Post subject: | Re: Tuning help |
Maybe motor is making more power at 4300 than at 4600. Stock carb with no special tricks is only going to pull up so far. Sure you can trim up and it will rev. 4300 and 30 mph sounds about right . |
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| Author: | Will C [ Wed Oct 11, 2017 9:07 pm ] |
| Post subject: | Re: Tuning help |
Also when I'm cleaning up the tip in bog I run the mid jets or "tip in" jets a little bigger and set the idle fuel normal. I think you need some more air man. |
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| Author: | MaXXis85 [ Fri Oct 13, 2017 6:10 am ] |
| Post subject: | Re: Tuning help |
Plug looks fine to be honest. No heavy soot, a full color on the base ring, and the heat rande seems fine. Most stock carb'ed, cammed, and exhaust motors will turn 4300-4500 depending on total setup. |
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| Author: | Heavyshot [ Wed Nov 08, 2017 10:34 pm ] |
| Post subject: | Re: Tuning help |
Finally got around to welding in the stainless bung for the hand held wideband and figured out it was super lean across the board. Mainly up top with readings in the low 20’s and around 17 at idle. I didn’t have any mains on hand to richen it up so I drilled them with the next size up that fit from my micro bit index and played with air screws again (cut tabs). I guess I got lucky because that got my wot afr to right around 13.5 at 4600rpm/33 bumping 34 and 15afr at idle. |
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| Author: | Will C [ Wed Nov 08, 2017 10:59 pm ] |
| Post subject: | Re: Tuning help |
Badass. Glad you found it and didn't keep runnin it. Watch cyl 2 plug for lean. 13.5 is the average of the two cyls so 1 is leaner than 13.5 and 1 is a little richer. You prob need a bit more fuel to be safe. Measure the drill bits your using so know where your at in thousandths and where your going |
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| Author: | Will C [ Wed Nov 08, 2017 11:09 pm ] |
| Post subject: | Re: Tuning help |
Too add a touch more fuel i would bump the tip in jets. Yours prob measure in the .016 to .017 range. I run .019/.020 in many. .022 is always too much. Engine will feel more responsive and you get your safety fuel. Also don't try to set your idle fuel with the gauge. There is usally outside air contaminating the reading and your ide will end up rich. Set them by feel |
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| Author: | Heavyshot [ Thu Nov 09, 2017 7:04 pm ] |
| Post subject: | Re: Tuning help |
I’ve got a IR laser thermometer on the way to check head/header temps. There is still a slight lean condition in the mid range but I’m guessing that addressing the tip in jet size will help with this as they overlap with the mains? It’s amazing how much better it runs so far. |
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| Author: | MaXXis85 [ Fri Nov 10, 2017 8:39 am ] |
| Post subject: | Re: Tuning help |
Will C have you measured cylinder head temperature at the spark plug with proper AFR at WOT? |
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| Author: | Will C [ Fri Nov 10, 2017 9:03 am ] |
| Post subject: | Re: Tuning help |
With an IR laser ,No sir I havnt .Efi you can watch cyl head temp. I like the idea though. I will drive , you hang off the back at WOT with the laser gun 
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| Author: | Russ [ Fri Nov 10, 2017 9:31 am ] |
| Post subject: | Re: Tuning help |
pics or it didnt happen. viral video in the making. #CFFITR #TheGhostBoat #whoneedsphysicsihaveamudmotor |
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| Author: | MaXXis85 [ Fri Nov 10, 2017 11:46 am ] |
| Post subject: | Re: Tuning help |
| Author: | Will C [ Fri Nov 10, 2017 2:09 pm ] |
| Post subject: | Re: Tuning help |
The outside air temp has more effect than a leanout. 175/200 normal run. I havnt thought to do an intensional leanout to to compare. But it will now be on my list. I look at the plugs for timing and heat. As I know you do too |
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| Author: | cb5331 [ Sat Nov 11, 2017 3:04 pm ] |
| Post subject: | Re: Tuning help |
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