XS hard to start after warmed up

[imofftothemoon]

Carbs are set to around 27mm, within 1mm+/-. Just cleaned them, checked the float valve seats and put new vitron o-rings on the float valve seats. Float needles look good. I have a brand new inline fuel filter on the bike.

I was having an issue with the carbs flooding due to a clogged float valve seat and I thought that was my issue, but it's still having this issue after cleaning them.

The bike will start relatively easy when cold with electric start and idle well, and it'll go down the street, albeit a tad rougher than usual but it stays running fine. However, if I turn it off when it's warmed up it's very hard to start again. I can sit there cranking the starter and nothing. I had to bumpstart it yesterday and that barely got it going, it was gurgling and only firing occasionally when i was bumpstarting it, but then after i got it cleared out it ran fine.

specs:
- non sight-glass motor
- BS34 carbs w/ 145 main jets, stock air jets, mix screws 4 turns out
- sock filters
- HHB CDI, new plugs gapped to .35
- open pipes

I noticed some possible oil leakage around the head, I think the head gasket may be blown. Could this be my issue?

 

[xjwmx]

If it's hard to start warm, try holding the throttle open while you crank it.

 

[Bob Kelly III]

That definitely sounds like a Flooding issue ! those are mighty big main jets !!!!!! but as long as it's burning correctly on top end keep'em
( do a plug color check, info in the tech section under garage at the top.)
usually this condition is caused by too high of a float level setting reduce the float level to 24MM instead of 27mm and see if that cures the issue.
and re torque the heads for the oil leak, that may stop the leak follow the torquing pattern in the tech section!
....also don't use the choke once warmed up only when cold.
Bob......

 

[imofftothemoon]

yeah the 145's are big but they've been working fine for me for quite a while and thousands of miles.

i'll try, but won't setting the float to 24mm raise it rather than lower it? i have brass floats too btw

 

[Paul Sutton]

If there is uncertainty about the float height then use the fuel level method. This is where you attach a short length of plastic tubing to the drain on the float bowl and see how high the fuel level is. When you have the tube in the correct position showing a fuel level I then lower the tube approx. 5mm and let the level re-establish to give a second check. If you search this forum, other forums, a google search you will find the full details and diagrams. Also with this method you do not have to remove the carbs unless adjustment is required.

For BS34s with brass floats I think the +/- part of specification is very tight so easy to over-shot.

 

[Bob Kelly III]

Yah ! listen to Paul that is a much easier way to check the float height the fuel level should be at the bottom edge of the float bowl gasket in the back.... if your engine is tilted back it will effect the float level you can run.
.... with your carbs upside down and float bowls off you measure float height from the gasket surface to the top of the float where the metal bracket holds them on, not way out to the highest point ( with plastic floats that should be the highest point.
so if you raise the float level you will reduce the amount of gas in the float bowl , you are correct ! lowering it will raise the level of gas
so my suggestion is just the opposite of what I was meaning for you to do ! Sorry , I'm human not perfect ! LOL
but check the fuel level in the float bowls first they may well be fine if their at the top of the float bowl but no higher you are good to go and something else is the problem, perhaps a weak coil that gives less of a spark when warmed up
..... I checked my float level with a 18" piece of 3/16" vinyl tubing and just plugged it on over the orifice on the float bowl bottom, held the tube along side the float and then opened the bowl drain screw about a turn. the level of gas going into the vinyl tube stopped rising right at the lower edge of the top of the float bowl
if the fuel level looks good check that your choke lever is actually closing off the choke sometimes they get sticky and will leave one or both slightly on this should show up in a plug color check but it won't if it doesn't do it constantly ( it'll burn off the over rich color reading when it doesn't stick open....) if you have the tank off take a VTOM and check the primary resistance and secondary resistance of the coil just for kicks and see if their within specks if not you may have found the problem.
it's a process of elimination , make sure one thing is correct then move to the next possible cause.
personally , I'ed run the brass floats , I trust brass much more than the plastic things !
good luck !
Bob..........

 

[Bob Kelly III]

What exactly are we dealing with here what year of motor ? you can find the engine numbers on the engine block under the right front motor mount and use it to look up the year it was made in the tech section at the bottom.
BS34CV carbs are on specials so I am assuming 1980 and up, I have a 83' with BS34CV's but mine is a sight glass type it could be an older motor with different carbs on it than were on it originally. hence the need to know the year.
all 80's and up had TCI ignition but yours has HHB-CDI which have problems that would be my next place to look after testing the coil.
.....
that is a Odd problem I will admit.... not many complaints like that one ! but it's gott'a be fixed it renders the bike useless ! no fun at all !
hang in there , you'll figure it out !
....
Bob..........

 

[imofftothemoon]

Yeah so several things,

1- i broke my last engine so i bought a new engine for my XS, it's a non-sight glass engine so i'm assuming pre-80's, but i'm still running my bs34's from my 80's engine.
2 - i have 6 over forks, so yeah, that could have something to do with my float levels. it only started doing this after i messed with the float levels trying to bring them to spec, they were probably fine as was. i didn't think about engine level in regards to float height. how severe of an effect will it have on oil level too?

I'll try to get the VIN for you, bob, i'm curious as to what engine it is too as the guy i bought it from states it came from a 80's titled frame.

 

[upthemaiden]

I had a Yamaha yz426 supermoto that had that problem at one point. It'd always start perfectly fine, but if I stopped it while I was out riding, and tried to restart it, it had no interest. Usually engines are easier to start when they're warm.

As far as your floats, make sure you check them with the clear plastic tube. My float started sticking the other week, did a rebuild with new gaskets, set the float height, still leaked. I eventually checked, even though I set it to spec, it was still leaking. Took a couple tries to checking it with the rubber tube to get it perfect.

 

[Bob Kelly III]

Indeed I set mine 4 times and tried 3 different settings as I could not determine which setting was correct for the 83's in the end I used the sight tube to see where the fuel level was and it was too high on one by a small amount using the proper settings.... so I changed just that float level and brought it down a tiny amount like 2mm max and tried the sight tube again and it dropped to a tad below the top of the bowl
I figured that was close enough and it was, she ran like a top after that !
.....
Bob......

 

[650Skull]

This subject has two major threads, active presently.................the float-level on the BS34's is extensively discussed and the advisers on here are/were actively involved with the thread and yet they don't give you the correct float height for BS34's and they are running them on their own bikes...............Why aren't you guys helping??????.

.

 

[Bob Kelly III]

Because we have no experience with this type of problem and are waiting for an expert like you to solve it for us !
so...solve it !
Bob........