Carb tune done with Cobra Slip ons

[ItsDuckie]

Well as the title says. I am looking for suggestions as to what fellow VMAXers have done with Cobra slip on setups. My bike is currently all stock with the exceptions of the slipons. My issue with the bike is cruising around 3.5k to 6.5k (around 65mph to 80mph or so) it studders and acts like it isn't getting fuel no matter what rpm i try to stay at. But if I roll the throttle it will pick up and go. I thought I had found some threads through some searching but I can't find them now. I just did a carb sync which took me forever as they were WAY out. And this problem has come back. Before I did they sync it was doing it so I added shims the the needles and the studdering went away. Before it would do it cruising around 45-50mph. They are stock needles. I am sure that is one of the problems. But not 100% sure. I know the Cobra slipons are terrible for the VMAX but I do love the sound. Don't have the money to throw down 600+ on new exhaust.

David

 

[one2dmax]

probably flooding, not starving

 

[Damon]

+1 to Sean,
This sounds like a case of the mixture being too rich! If your stumble is in the range of 4000RPM ~ 5000RPm I would be removing any type of shims from the stock needles, & back down on the fuel mixture screws. The Cobra's generality work well (- a few ponies) with a completely stock carb setup, but can provide good throttle response.

 

[ItsDuckie]

Well I guess I will take off the shims and see what happens. I believe I have the mixture screws set around 2 1/2 to 2 3/4 turns out.

 

[Traumahawk]

Yep....the shims RAISE the needles so they move out of the main jet quicker, and give more fuel. They probably dont need any shims at all.

 

[veebooster]

You may have to jet down one size on the mains as well.

 

[ItsDuckie]

And that would be 147.5s correct?

 

[alorio1]

Stock is 152.5, but I don't know what increments jet sizes are but I would guess you will be going down 3 sizes, that just my guess now. Maybe someone else will chime in to verify.

 

[Traumahawk]

Stock is 152.5, but I don't know what increments jet sizes are but I would guess you will be going down 3 sizes, that just my guess now. Maybe someone else will chime in to verify.

Stock is 152.5's, 1 down is 150, 2 down is 147.5's......so each step is 2.5 either up or down.

From a performance stand point, the Vmax is 1 step RICH from the factory....so you could go to 150's.....or the 147.5's. Sean has said before its really tough to get a Vmax TOO lean.

 

[veebooster]

And that would be 147.5s correct?

Traumahawk's got it right. 2.5 increments. You'll have to play with it to get it right. That can be fun and frustrating at the same time. There are carb masters on this forum who can help alot!

 

[one2dmax]

145-147.5's

 

[ItsDuckie]

Well, not 100% sure, but I think it is now doing it cruising aroun 45-55mph. It was kinda hard to stay steady for any length of time due to stop and go. I took out the shims before I left work. Was not able to get on the highway. I will try to take a test ride later today to be 100% sure it isn't still doing it.

 

[ItsDuckie]

Took the highway tonight on my way in to work. Seems to still be the same if not worse will riding on the highway around 65-80 mph. Looks like I am going to order a few different sets of downsized mains. Would any one suggest changing the pilot jets at all? Just want to check before in place an order for the mains. Gonna order 145s and 147.5. Thanks everyone for the tips.

 

[Traumahawk]

Nope....as long as you still have the stock airbox...and the stock pipes...just changing the main jets is fine.

Sent from my PB99400 using Tapatalk 2

 

[ItsDuckie]

Ok. Little update. Finally got some main jets and time to install a set. I bought 147.5s and 145s. Installed the 147.5s yesterday and ran out of time to test drive it. Had to leave for work. I just took the bike for a ride and it still does the same thing and I really feel that it is worse. Having a hard time understanding how/why there is no improvement. Seeing as I went down 2 jet sizes. Gonna let the bike cool down to pull the plugs and check the color of them before I head to bed for work. I will install and try out the 145s. But after what I seen with the 147.5s my hopes aren't high.


Duckie

 

[sdt354]

I'd bet you've got something else going on there. Check the float levels-wet. If you have to remove the carbs. you might as well go through them. Or, box them up and send them to Dannymax, and kiss your carb. problems good by.

 

[ItsDuckie]

Left to right. 1 thru 4

 

[ItsDuckie]

I just recently went through them. New jet block plugs, gaskets, orings and float needle. And float has been set per the dry method. Havent had a helping hand to help me keep bike level to check wet levels (PO before my uncle removed and ground center stand brackets :bang head::real mad: ) I am also not 100% sure how o do it. Instructions in book are pretty vague. Especially when it says get tube of suitable length.... Uhhhhh ok? LoL What is suitiable length?!

 

[thor_eyerdhal]

Long enough to put it against the carb side (near the pointer), it can't be too long

 

[sdt354]

I just recently went through them. New jet block plugs, gaskets, orings and float needle. And float has been set per the dry method. Havent had a helping hand to help me keep bike level to check wet levels (PO before my uncle removed and ground center stand brackets :bang head::real mad: ) I am also not 100% sure how o do it. Instructions in book are pretty vague. Especially when it says get tube of suitable length.... Uhhhhh ok? LoL What is suitiable length?!

4" will do. Cycle the key to fill the bowls. Put a jack under the bike to hold it upright. Mark the tube 17mm from the end. Hold it up to the line, with the drain open. turn the key back on. Make sure you bleed any air out of the tube. Observe your true float settings. The clear tubing slides over the black drain hoses. Take the black hoses out of the bracket holes first. If I forgot something,which is easy for me, someone else will chime in.