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Mikuni running best at 3/4 throttle
http://mudmotortalk.com/mmt_v2/viewtopic.php?f=3&t=20125		 Page 1 of 1
Author:  bbb [ Mon Jul 18, 2011 10:52 am ]
Post subject:  Mikuni running best at 3/4 throttle
I can run up to 3/4 throttle fine. Anything more and it begins to bog down.

Any reason for this? Any problem with this?

I'm hoping to have the Iron Mountain heads in this week, so should I just wait to mess with the carb until I see what the heads do for it?
Author:  drake1 [ Mon Jul 18, 2011 10:56 am ]
Post subject:  Re: Mikuni running best at 3/4 throttle
More than likely to big on the main jet.
Author:  cb5331 [ Mon Jul 18, 2011 10:58 am ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Take a look at this thread and see if it helps any. Specifically Bayouboy's post.

viewtopic.php?f=3&t=19491&start=0&hilit=throttle+slide
Author:  BoatDR [ Mon Jul 18, 2011 11:08 am ]
Post subject:  Re: Mikuni running best at 3/4 throttle
How long ago did you install the carb kit?

I had 2 motors come in last week with the same complaint, and both had a tear in the prefilter and the air filters were clogged up with mud. Although both had 200+ hours on their motors since they had the carb kit installed. Try running the motor for a quick run without the air filter installed, and see what happens.
Author:  bbb [ Mon Jul 18, 2011 1:51 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
I've had the Mikuni on for about a year and it started doing this bog down stuff a few months ago. We don't run mud at all over here and I had the filter and pre-filter off yesterday and both were real clean.
Author:  bbb [ Mon Jul 18, 2011 1:59 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Author:  WestEndAngler [ Mon Jul 18, 2011 2:05 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Author:  cb5331 [ Mon Jul 18, 2011 2:06 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
I run the Autolite 3923 - gapped at 0.35. This is the plug that DB8 recommends a lot.
Author:  BoatDR [ Mon Jul 18, 2011 2:10 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Author:  BoatDR [ Mon Jul 18, 2011 2:47 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Author:  drake1 [ Mon Jul 18, 2011 7:18 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
I like Denso IQ20 for modded motor and IQ22 for stock. Gapped at .030
Author:  bbb [ Mon Jul 18, 2011 7:38 pm ]
Post subject:  Mikuni running best at 3/4 throttle
Author:  deadbird8 [ Mon Jul 18, 2011 8:18 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
If it ran fine before then run it without the air filter Like BoatDr said and see if thats the culprit. You will run a little fatter in the heat of summer but if your main was too large, it would have probably been doing the same since you installed it.

I don't think this is your problem but will add it if anyone hits this on a search later. I had a drop off after 3/4 throttle after installing mods and changing coils. I put the A/F meter on it and found out I was running really lean in the mid-range and the main was fine. Adjusted the needle clip position and it brought it back in range.
Author:  bbb [ Mon Jul 18, 2011 8:34 pm ]
Post subject:  Mikuni running best at 3/4 throttle
Heres a dumb question. I went outside and took the filter off the motor to see how high the slide was going up. It does go all the way up and then some. My question is, should fuel be spraying out the back when I squeeze the throttle? The needle at the rear of the carb sprays the fuel out the back. Is this right or should it be adjusted.

Luckily the stream hit me in the neck and not the eyes. I was not expecting that.
Author:  craig [ Mon Jul 18, 2011 8:38 pm ]
Post subject:  Mikuni running best at 3/4 throttle
Yes, that's normal.
Author:  bayouboy [ Mon Jul 18, 2011 10:46 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Uh, Is it shooting in and hitting the jet needle then coming out? If its shooting straight out than your accelerator pump nozzle is facing the wrong way. It should shoot in and hit center of the jet needle. If it is shooting staight out then it needs to be turned 180*, just take a pair of needle nose pliers and spin it around. I'm pretty sure I'm miss reading it, Thats very rare! Plus you would have fuel dripping out your fitler everytime you throttled up.

What exhaust are you currently running? Oh never mind I just read your sig! Sometimes if you go from a high flow exhaust (with an after market carb) to a stock one it will cause the carb to cough at wot. You have to get out what you put in. ;)
Author:  craig [ Mon Jul 18, 2011 11:04 pm ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Shit...I read it wrong! If it's shooting out of the back then it's facing the wrong way.
Author:  bbb [ Tue Jul 19, 2011 7:36 am ]
Post subject:  Mikuni running best at 3/4 throttle
Yep sprays straight out the back of the carb. Funny thing is I just came back from running it on the trailer and it runs fine like that. One you throttle up, the spray is just sucked back into the body. Kinda makes you nervous though with a hot muffler, open carb and fuel, all a few inches from each other.

This was my fault though. When I was inside the carb trouble shooting it Saturday, I remember turning a brass object with a flathead and wondering why it didn't do anything. Then i put everything back together and ran the lake with no problems.

Maybe it's not super important which way it's spraying, but I'll definitely get it turned back the way it was.
Author:  bbb [ Tue Jul 19, 2011 10:55 am ]
Post subject:  Re: Mikuni running best at 3/4 throttle
Got it turned back around and spraying back into the carb. Makes alot more sense this way. :D

Got come carb cleaner sprayed in it and treated the gas with Seafoam.

Cranked it up on the trailer and it sounds like its back to normal.
Author:  bbb [ Tue Aug 02, 2011 7:45 am ]
Post subject:  Mikuni running best at 3/4 throttle
Did a couple things and got the motor running right again.

Installed the Iron Mountain head, added oil(1/2 quart low), changed the spark plugs and fixed the little thing in the carb throat from going so high.

I'm sure it was the last thing on the list, but throttle is not sagging anymore at the top.
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