Help jetting

[mml03102]

Another post by me! I recently changed to a spiked air cleaner and I went up to a 76 main jet and it helped some so I went to a 78 as s&s suggest. runs great until it gets up to about 70 then it keeps losing power until you give it a llil throttle . I read post here and they said something about an air bleed, should I change that or maybe go up another notch to an 80 main jet. I hate to be a post whore but I can use your help also if so on the air bleed , would I go up in size like I did on the main? :flag:

 

[Srodden]

Sounds like an air bleed issue never heard of needing to go to an 80 jet. The air bleed controls when the intermediate and main jet switch usually it's around 70 mph some like to change it so it will switch at a lower speed due to highway cruising.

I'm not sure whitch way to go I think it's up to a 50 ? Air bleed do research from S&S. You have to pull the bowl to do it.

 

[DRBarnhart]

I recently changed to a spiked air cleaner and I went up to a 76 main jet and it helped some so I went to a 78 as s&s suggest.

Just curious where S&S suggests that? Your engine isn't backfiring and breaking up in the carb right? Wouldn't it be better defined as "going flat"? And if that's the case you go down a main jet size...

Just curious...

Dennis

 

[DRBarnhart]

Sounds like an air bleed issue never heard of needing to go to an 80 jet. The air bleed controls when the intermediate and main jet switch usually it's around 70 mph some like to change it so it will switch at a lower speed due to highway cruising.

If his engine runs great until it's running on the main jet doesn't it seem like it's main jet problem? It runs OK when he hits the throttle and considering all he's doing there is adding more air, there must be too much fuel...

:up: or :down:

Dennis

 

[Mickeetwo]

Turn your spike air filter vertical and you will not have this problem.



Once you get it dialed in the weather will change and the problem will return. On hot days with low humidity mine would run good. On cooler days had the same problem. Got tired of messing with it and turned my spike air filter vertical and no more problems with the flat spot at 68mph or 70mph. I was told it has to do with the spike air filter deflecting the air at this speed. Not sure if it true or not, all I know is when I turned mine vertical the problem disappeared and has not returned. Been running mine vertical for a couple of years now.

 

[mml03102]

t it says . To test the Main Jet, do a roll-on from 50-mph to 70-mph in 3rd gear. If the engine back fires or breaks up in the carb, increase the Main Jet size .004”. If the engine is flat or will not accelerate, decrease the Main Jet by .004”.
I guess going flat would explain it but it is fine when you accelerate , just cant hold a steady speed and when I increased the jet size it did get better but not 100 percent . I will read up on the air bleed , guss I will need a gasket for the bowl?

Sorry I meant to say increase the size od the main jet!

 

[francoblay1]

Marc,

Send me an email, I will give you some info.

 

[DRBarnhart]

I will read up on the air bleed , guss I will need a gasket for the bowl?

Dennis

 

[aspen874]

I had the D&M spike on my Mastiff, while trying to cruise at 70 mph it would hesitate, I couldn't solve by Jetting. There are other members here who have had the identical same problem with the spike. Some have turned it vertical and the problem went away. I can't speak about the air bleed, hope someone here can help you with that. I elected to change mine to the S&S dual runner, zero problems after that.

 

[Srodden]

If his engine runs great until it's running on the main jet doesn't it seem like it's main jet problem? It runs OK when he hits the throttle and considering all he's doing there is adding more air, there must be too much fuel...

:up: or :down:

Dennis

Sounds like at 70 he's in between the intermediate and main jet. I'm just guessing from a distance personally I would have to run a complete carb adjust per S&S instructions in person to diagnose.

You can cover up some issues by running too rich but never solve your root problem.

 

[mml03102]

There was popping on decel and flat at higher speeds so I went to a 076 and it improved some then I went to a 78 main jet and it is fine until you hit the highway and it goes flat at times but even better now after going up one again on the main jet . I just read s&S again and they suggest going up 1 on the main jet air bleed if its going flat after changing the jets so I will pick one up from the hd dealer , should I also go up one on the intermediate while Im in there?

 

[mml03102]

I went from a 31 to a 33 as suggested by the techs at R and R cycle and Im able to hold steady speeds on the highway and Im getting around 33 mpg!