Carb questions

[dug050]

I have a 1996 Royal Star that I bought two summers ago .The bike has always had an issue with backfiring from no.3 cylinder on cold startup and that pipe is slow to warm up.

I thought it may be a bad coil but when I swapped two coils around the problem stayed on that same cylinder. The bike is away for the winter so I decided to pull the carbs and when I did I found that the no.3 carb was not seated properly into the boot. The boot was bent in on one side and likely causing a vacuum leak. This may have been the problem but I decided I would check the float levels and jets while I had the carbs off. The previous ower said he had rejetted when he installed a K&N filter and as far as I know that is the only mod he has done. It still has the stock pipes and no signs of any drilling of the baffles. I read the article about rejetting in the tech section and they changed the pilot jets to 17.5 from 15 and the main jets to 125,125,120 and 122.5.

The pilot jets in mine are stamped R,followed by a square,20 and all the main jets are stamped R,followed by a square, 95.

The bike always ran well but these jet sizes are different from anything I have read and I don`t know what the previous owner was trying to accomplish. Should I be changing these back to the stock sizes or at least the sizes shown in the tech article for optimum performance.

Any comments would be appreciated.

 

Doug

[dug050]

Just went to the Bike Bandit site and it looks like the jet sizes for the Royal Star are different from the RSV. It looks like all stock jets in mine.

I would still appreciate comments on whether the carb not being seated properly could have caused the backfiring problem.

Thanks

Doug

[Pam]

I am no expert but I would think that if the carb is not seated properly and the cylender is sucking air it will be causing a lean condition, That should show on the plug. just like a car engine. As for the jets I have no clue on that

 

frank

[V7Goose]

Yes, a carb not seated properly could cause that problem.

 

I'd double check your carb part numbers and jet sizes against the Yamaha parts breakdown. I do not have personal experience with the early Royal Stars, but I thought they had smaller carbs and all the same jet sizes, where those jet sizes you listed sound like stock RSV jets to me (haven't tried to look them up - just sounds familiar). The part number for the carb body is stamped right on them.

 

Correction - those jet sizes are NOT for the RSV, just like you said; they are all bigger. But I cannot say if they are right for your bike.

Goose

[gunkylump]

Hi Doug!

 

I'm no expert...but if the carb wasn't seated in the boot properly....it will definitely affect performance in some way. You probably wouldn't have the vacuum needed to pull the gas in to the carb as it should?

 

I have the k+n air filter in my 96, and I did not rejet the carbs, and it always ran fine, in fact gives me awesome gas mileage.

 

Were the floats set in the proper position, and the carbs clean? If so, I would suspect that now you have the carb seated properly, your issue will either disappear or be gone altogether. Are the carbs synched?

 

That's my two cents.....I'm sure a real techie will chime in shortly.

 

Merry Christmas my friend!

 

gunk:Laugh:

[V7Goose]

A quick glance at the Yamaha parts catalog for the 96 Royal Stars seems to show that all four of your main jets should be 95, and you pilot jets should be #20. I went back and re-read your first post and finally understand that is exactly what you said was in there. I did not understand that the other jet sizes were just what you saw in a different posting. So I agree - your jets look stock size; therefore, I'd assume your carbs are the correct ones, too. I think all you need to do is make sure everything is clean and all the rubber boots are properly attached when you put it all together. I would also check the current settings of the mixture screws and make sure they all seem to be set close to the same.

Goose

Edited December 23, 2010 by V7Goose

[dug050]

Thanks for your replies. I have checked all the jets and everything looks clean. Just have to check the float heights and put everything back together. I will also be checking the valves and resyncing the carbs before Spring.

Hope everyone has a Great Christmas!!!

 

Doug

[Pam]

I forgot to mention in my other post. I had a similar issure with my 83 VR. it was a cracked carb diaphram. The bike would labour along and pop and all of a sudden come alive for a while. Changed the diaphrams and a carb sync and away we go. But that was on an 83 yours is considerably newer.

frank