help please...

As you know I have exposed carbs on my bike... however nice day yesterday so decided to have a play... riding around town all day at speeds of 30-50mph with no problems...


now problems start when I go over 60 for any length of time... its like its fuel starved..

it will cut off and die... leave it 10 minutes and its ready to ride all day at low speeds....

Am I right in thinking its the carbs set up... I have to have cones on as there is no other room so any advice or suggestions.. .please help

 

This sounds more like a fuel delivery/ fuel tap/filter problem.

If it was the lack of air filter, I would think the problem would go away as you slowed down?

Another important point is: Can air get into the fuel tank? Is the cap vent blocked? This would starve the fuel.

Hope this helps.

 

at slow speeds it runs great... its only at high speeds it runs badly.

or not at all

the tank is totally differant and is no longer the same ... its a custom job and I am sure it is able to get fuel through... but will check on that point.. I will also check the two filters... which one is on the fuel tap and one is inline to the carbs...

 

How did you set your float levels? It does sound like it's simply unable to keep up with demand; if the filters aren't plugged and the fuel tank has an operational vent, then I would look at the floats.

The first thing I would do though is to simply pop the gas cap open the next time it starts to happen...

 

did you ever check the valves

 

hey that's my line...

(the most ignored/glossed over question on the site. Ever notice how many times it's asked and simply ignored? Like the valves themselves...)

That is also a good possibility.

 

Do these carbs have the propensity to succumb to carburetor ice? Carb ice can happen when ambient temps are around 60 with high humidity. This places the carb venturi around freezing.

 

Right tank is fine.. fuel is fine.. ish.. needs a clean out since new tank went on.. but will check both filters again..

The carbs are the normal standard carbs.. I only put those K&N filters on... I would have thought that the air fuel mix would be maybe out a bit... but thanks so far for the posts above.. will be checking all the above.

I also have short exhausts on... but as stated.. it does seem that it could be a float issue.. at low speeds all is fine.. but seems to be draining it all when at higher speeds... for a sustained time.. ie more than a quarter mile.... but will happily plod along all day every day doing 40-50 mph.. sadly it has to do at least 70 on long roads here.. and YES MPH not KH lol.

Thanks everyone again.. I had alot of thoughts in my head like are coils getting hot.. is a lead burnt out.. is there water in my carbs... and so on.. but I realise it cant be anything too serious.. and I know these are a MONKEY to set up with these filters on.. but I didnt know if I needed a larger Jet.. or what.. so any help still to come I more than welcome it.. expecially from anyone who has fitted them.. (just cause they know if it will work) cant see why not myself... as I dont it on enough piggen bikes before...

 

Chacal has a section in his 'XJ4Ever Supporting Vendor' forum that has a set of basic "formulas" to use as a starting point when jetting for pods. http://xjbikes.com/Forums/viewtopic/t=1 ... art=0.html about 1/3 of the way down the first page.

Yes, they CAN be made to work. They will never have the complete flexibility and response in all ranges that the bike did stock, but you can get close. The problem is that CV carbs cannot perform at their utmost with an unlimited supply of intake air. They are designed to work within the physics of a finite air supply; there is much debate about this, however-- do a forum search on "tuning for pods."

One caveat to this whole fiasco though-- EVERYTHING ELSE about your carbs has to be 100% right before you start trying to tune for pods. It WILL NOT work if there is another problem screwing with your results, like uneven float levels, or being out of sync.

 

that is AWESOME advice.. thanks for that link... will be trying to calculate the jet size and then order it from him.. cheers bud.. I appreciate your help.

 

Too much air being forced through at higher speeds-fuel cant keep up.
Very simple.

 

its not really being forced through.. I guess I will go on the defensive for those with cones... I owned ALOT of bikes.. and MOST have had cones put on.. setting up the carbs is a bit tricky I will admit but you will find a ballance.. the YICS engine is a little bit trickier... (spelling??)

but its getting starved of fuel.. it wouldnt cut out at higher revs Parts... it would just not perform as well... and because the air filters and the exhausts ballance each other out.. the actuall running is fine... I have been searching to see if the tank is vented... it is!

now I have two filters to remove.. easy you would think but it means stripping the top half off to get at them.. arrgh... will be about a 2 hour job that.. but will check the filters next... btw the floats are fine and the carbs are still clean... ie no crud in them and the needles appear fine.. not bent or sticking.

so it has to be a issue with the filters... maybe just one might be a good idea.. I could be starving it by having two on... who knows?

I will keep you all updated.. but thank you all so much thus far.. you have really been a great support...

 

Right. But have you verified, using fuel and the clear tube method, that the float levels are in spec? This is going to be an important part of getting it correctly jetted for pods, and exactly the type of thing I was talking about. 100% not 90%. "Appearing fine" is not 100% verified; if you've got even one carb with a high or low float level you're starting off handicapped.

 

Fitz... the carb levels are 100% fine... I am going on the assumption that there is a blockage at this point..

then I will be looking at re jetting the carbs for the "fine tune" as the jets in at the minute work... it just the fuel starvation that is the issue... by rejetting the carbs wont increase the fuel going to them... which is where I am believing the problem to be at the minute..

 

Oh, it sounds like re-jetting is in your future. From your description, said "starvation" occurs once you actually get up on the MAINS and need to feed some serious fuel; you're fine running off the pilots at lower speeds/rpms.

 

2 filters sounds like a lot of restriction for a gravity fed fuel system.

I'd try it with straight line just to see what happens, just to eliminate the simple and obvious as a cause...

 

Two filters are what any XJ with an inline fuel filter is running; there is the "gauze" pre-filter atop the petcock, and whatever inline filter was installed.

That in and of itself should not be a cause for concern unless one or both are plugged.

 

OK...didn't realize he was referring to the strainer.

 

my petcock is a harley one.. with the metal mesh etc.. and its a filter... then I do have a inline one about 4 inches below that..

again kinda same set up...

will need to work on the ideal jet size for my bike... argh..

thanks again.. thats exactly what its doing.. but surely by putting a larger jet on.... it still wont increase the fuel thats in the carbs... will it? because what appears to happen is its using up all the excess petrol in the carbs on the main jet and then running out... ..

 

I have just sent chacal a pm asking for the main jets... hopefully this will help improve and make my bike work at high speed... I am trying to work my head around the logic but hey.. go with the flow if you ask me!!