Warm Running Issues

[theman4444]

Hello fellow KatRiders,

Very new here, so please be nice.

Bought my 1995 Katana 750F (GSX750F) late last summer 2012.When I picked it up it ran fantastic and only had a problem with the blinkers that I sorted out and now they work fantastic.




It took me a week or two to figure the blinkers out and get it titled and everything. I was able to ride it one blissful day to school and back again 30 miles. The next day it didn’t start and also had a fuel leak which looked like it was coming from the carbs. I knew the leak could be anything so I decided to do things one step at a time. As you can tell from the blinkers I’m a DYI guy at heart and have replaced an engine at one time so I thought I could take this on.

The next day I pulled her out again and got her started up after lots of coercion. She appeared to have developed a hesitation and seemed to be flooding out so badly that there was fuel in my airbox and also ran very poorly. The throttle response was gone and the revs were either extremely high, or so low that it was about to die. I went ahead and checked compression and was getting good numbers. I also checked spark and it appeared that it was sufficient. So my mind went to fuel.

At this point I had never seen what the carbs looked like but I thought there was a chance they could be mildly clogged so I put a nice amount of seafoam into the tank and also sprayed down the carbs with seafoam. I let that sit for a couple hours and started it back up after tons of coercion and lots of smoke. There wasn’t much of a change in how the bike ran so I decided that I would have to rebuild the carbs.

I took the carbs off and drained them but life happened and I wasn’t able to work on them until last week (Dec 2012). I left some of the seafoam in the tank to act as a stabilizer and it seems to have worked well. I pulled the carbs apart and went through them pulling the main jet and other metal pieces and soaking them in carb cleaner. I went through all of them but the crazy thing was they looked super clean without any gunk at all!!! I also checked all the float heights and they seemed perfect at 14.6 exactly! It was nice to see that they were still in good condition but a little unnerving as there wasn’t much for me to fix.



So I went ahead and put them all back together and threw them back on the bike to see if there was any changes. It took a second to get the fuel through but it started right up again. It ran decently but I noticed that I had a HUGE fuel leak coming from MOST of the carbs!! I immediately ordered new float bowl gaskets and new front and rear float o-rings to replace any that were too hard.

Today (12/19/2012) I pulled the carbs again and replaced all the gaskets and o-rings in all the carbs that weren’t sealing properly and threw it all back on the bike. Took a while to start again, but she started right up. Perfect idle and no fuel leaks! She even revs like a katana should!!! I took her for a spin and she pulled like nobody’s business and was very fast. No hesitation or anything. I thought I was home free!!!!!!!!!

So I got about a half mile down the road and she started to lose power. Then she started to sputter out and die while driving. I pulled in the clutch and she died all together. This was very frustrating as she had been running so well since I started her up! I immediately tried to start again but only cranked and no fire. I checked and I had a quarter of a tank of fuel left and I switched the petcock to all different combinations but no change. So I started the push-of-shame as I made my way back to my house. Every five minutes I tried to turn her over but still no fire. About 15 min and about 100 yards of pushing later I cranked her over and she started up again. I limped her back home as she was already trying to die again. Once home I inspected and found there was still no leaking, which is good but it appears I have a warm running issue. I let her sit for an hour partly in contemplation and partly in frustration. I started her back up again and she starts up and runs with a great idle but has a really bad hesitation when I try to get the revs up. I opened the tank and let it run to see if it was vapor lock but the hesitation was still there. I’m not sure how else to check for vapor lock.

I have no idea where to check next. I’m probably going to spray the throttle slide with some WD40 to see if it helps with the hesitation but I’m not sure what is causing the warm running issue.
After checking the forum I have some ideas about what could possibly cause the problem like:

1. Blocked tank vent causing a vacuum in tank.
2. Something else restricting the fuel flow.
3. Heat causing an electrical component to fail (coil).

I feel SO CLOSE to figuring out what the heck is going on. I don’t want to scrap this bike but I have only ONCE been able to ride it without problems. PLEASE HELP ME!

[TRPUT]

Mate - with a great run down like that, someone with a lot more knowledge than I will get you sorted quickly. Things to check / know first:

Petcock positions - Down = ON / Forward = RESERVE / Backwards = PRIME

Is there a fuel filter between petcock and carbs? If so, lose it.

Ensure the petcock vacuum line from #4 carb is connected.

Petcock screen may be dirty - try removing from tank and inspecting.

Ensure you are running a clean OEM air filter.

Float needle valves may not be sealing correctly.

Have the idle / mixture screw plugs been removed so the screws can be accessed, cleaned and adjusted?

Beyond that is beyond me. It does sound fuel related - although checking plugs, leads, coils and connections won't hurt. (Most "electrical faults" occur in the carbs!!! )

[KatanaGSX92]

And Welcome to KR!

[jmd32477]

Someone here can definitely help you. Welcome to kr! Hope you get it sorted out.

[Badfaerie]

We had this problem on my 600 at one point. The culprit turned out to be the fuel lines. As the engine heated up they would get soft and collapse, it happened more often when my tank was less than 1/2 full.

The next thing to check, which is something you want to do anyway, is your oil. If your carbs were leaking and fuel was getting into your airbox it is 99% that you dumped fuel into your oil as well. If it is showing over full in the window that is the first indication, opening the fill cap and smelling fuel would be the second indication. An oil change would be an advisable step anytime you have carb flooding problems.

Just a note: There are some here that will argue that fuel in the crank case will evaporate after a short period of time and not be a problem. That is not my experience. I have troubleshot and fixed and worked on a bike for weeks only to have the problem solved by an oil change. So believe who you want, but ask yourself if a possibly prematurely needed oil change is worth weeks of headache and troubleshooting.

Finally, you might want to use my husband's trick to test to make sure your float needles are seating properly. With the bowls full, remove the fuel lines from the petcock and blow into them. If you can move air and hear it bubbling in the fuel, you want to re-clean/check/replace your float needles and float heights.

[theman4444]

Oh man, so many replies! It MUST be Christmas time! Thank you everyone for getting back to me so quickly, and having so many good ideas.

Petcock positions - Down = ON / Forward = RESERVE / Backwards = PRIME

Is there a fuel filter between petcock and carbs? If so, lose it.

Ensure the petcock vacuum line from #4 carb is connected.

Petcock screen may be dirty - try removing from tank and inspecting.

Ensure you are running a clean OEM air filter.

Float needle valves may not be sealing correctly.

Have the idle / mixture screw plugs been removed so the screws can be accessed, cleaned and adjusted?

Beyond that is beyond me. It does sound fuel related - although checking plugs, leads, coils and connections won't hurt. (Most "electrical faults" occur in the carbs!!! )

Thanks for the info. I do know the petcock positions but my fairings were off when I got stuck so I tried all the positions just to make sure that wasn't the cause. There is no aftermarket fuel filters in line between the petcock and carbs.

The vacuum line is connected to the petcock but I will double check it is connected to the carbs correctly.

Haven't checked petcock filter, will do that later.

Air filter is oem and shouldn't be an issue.

Haven't checked the float needle valves, will do later.

Idle/mix screws have never been adjusted ever so I didn't touch them. I don't think this would be a problem since it's all stock.

We had this problem on my 600 at one point. The culprit turned out to be the fuel lines. As the engine heated up they would get soft and collapse, it happened more often when my tank was less than 1/2 full.

The next thing to check, which is something you want to do anyway, is your oil. If your carbs were leaking and fuel was getting into your airbox it is 99% that you dumped fuel into your oil as well. If it is showing over full in the window that is the first indication, opening the fill cap and smelling fuel would be the second indication. An oil change would be an advisable step anytime you have carb flooding problems.

Just a note: There are some here that will argue that fuel in the crank case will evaporate after a short period of time and not be a problem. That is not my experience. I have troubleshot and fixed and worked on a bike for weeks only to have the problem solved by an oil change. So believe who you want, but ask yourself if a possibly prematurely needed oil change is worth weeks of headache and troubleshooting.

Finally, you might want to use my husband's trick to test to make sure your float needles are seating properly. With the bowls full, remove the fuel lines from the petcock and blow into them. If you can move air and hear it bubbling in the fuel, you want to re-clean/check/replace your float needles and float heights.

Great suggestion with the fuel lines. I never thought of that! I will replace them first and see if that makes a difference.

I have to admit that I have not changed the oil since I got the bike seeing as how I have only ridden it a total of 32 miles since purchase so that is also a really good idea. I never thought about fuel getting in there. After changing out the carb gaskets I never saw any more leaking of fuel into the airbox so I'm guessing I've stopped anymore fuel from getting into the crankcase. I will definitely change the oil along with the fuel lines.

Once I get done with some of these easier suggestions, I'll work my way to the hard ones.

[TRPUT]

Good call on the fuel lines - I had that issue for a while too due to new lines kinking when hot so definitely worth checking.

If the mixture screws have never been set since factory - it will definitely be worth investigating. (It appears they were never "set" at the factory in the first place - just inserted.)

[arsenic]

I agree, the A/F screws HAVE to be set at 2.5 turns out. They aren't really "set" at the factory and they are always extremely lean. Your thinking that they are stock so they can't be an issue is flawed. They MUST be set.

[theman4444]

Lots Done Today!

SO today was a long day, I got lots done but not everything. Forgive me because it snowed last night and it was freaking cold in that garage so it took a while to do anything in the subzero temperature.

1. I dismantled my bike... again.
2. I took off the fuel tank and set up a vacuum system on the petcock to check each of the positions for functionality (read: I hooked up a hose to the vac port and sucked on it while I changed positions in the petcock) There was lots of fuel dumping out in the "On" and "Res" positions so it seems that it works perfectly. I guess I can cross off the petcock on the list of things to check.
3. I sprayed WD-40 on the throttle slides. The slides were still a little sluggish, but once the garage heated up, the rubber became softer and the slides moved a lot easier. So I'm guessing that when the bike heats up this will not be an issue.
4. Took the carbs off and inspected the vac line. This looked really good without any signs of wear and tear and its placement on the carbs was perfect. No problem there that I can see. If I still have the problem I might change this out as a last resort.
5. Went to the store and bought fuel line, oil, and oil filter.
6. After getting home I tried the trick to test to make sure my float needles were seating properly by blowing into the fuel lines. On the longer hose going to carb 3 and 4 there wasn't any fuel in the bowls so the test was inconclusive there but on the shorter hose going to carbs 1 and 2 it held pretty well. Since the test was inconclusive on the one side I went ahead and checked/cleaned all the float needles for proper seating. I was fairly certain the float needles were seating correctly because I turned the carbs upside-down and tried to blow into the hoses and I could not get any air whatsoever into the bowls. I then went through each of the carbs and double and triple checked each of the floats and made some minute changes to float height to get as close to 14.6 as possible.

Here's a picture of the carbs with the old fuel lines coming off:

7. I then replaced the old fuel lines with the newer ones which were a pain to get on I might add. Then I strapped the carbs back onto the bike.

Here's a picture of the new fuel lines:

Carbs going back on the bike.



8. It took me awhile to change the oil because I couldn't find a pan thin enough to fit under the dang bike. I ended up using a paint roller pan and then emptied it into a larger pan when it got close to getting full. Oh man am I glad that I changed the oil, if that's what you could call this stuff coming out of my bike! It was thick and dark like grease and had a strong smell of fuel to it. I'm not sure how the bike was running before this with that nasty sludge in it.

A picture of the sludge:





9. After getting the new oil filter and putting new oil in I put the bike back together enough to try to start it.

10. I rolled it outside and turned it over about a hundred times until the gas and oil started to circulate through the necessary passages. It started up again! Thank goodness.

It was 20 degrees outside with snow on the ground but I drove it around the backyard a little and it seemed to be doing ok. I'm not sure if I fixed it as I wasn't positive I got it warm enough for the problem to happen. I didn't want to chance it on the streets when all the melted snow would be turning to ice so I'll have to try it again tomorrow after it warms up a little.


But for everyone who has helped me so far I have a little present. I took a little video of it running and showing the throttle response.


Sorry for it not being longer. It was really really cold out. You can see the snow on the ground.

[ame]http://youtu.be/ppvldoWfyXQ[/ame]

[TRPUT]

Have those carb-head boots got silicone on them??? And not sure if it is the photo, but #2 looks out of shape??? I reckon I would remove the silicone and check that they seal properly.

Also watch carefully as you install the tank to ensure the new fuel lines settle into position without kinking - the length has to be just right.

But, it sounds like you're having fun and making progress.

[Badfaerie]

Sounds like you are on your way. There may be a few things you'll need to check and/or tweak, but until you can get it on the road and warmed up you can' be for sure what the next step is.

[theman4444]

Have those carb-head boots got silicone on them??? And not sure if it is the photo, but #2 looks out of shape??? I reckon I would remove the silicone and check that they seal properly.

Also watch carefully as you install the tank to ensure the new fuel lines settle into position without kinking - the length has to be just right.

But, it sounds like you're having fun and making progress.

The Carb-head boots were left open to air for a couple months until I could get to working on the bike again, so I taped over them so nothing nasty could get inside. What you are seeing in the picture #3 is a very small amount of some leftover sticky residue from the tape but its only superficial on the outside. The carbs don't really even touch it but if this time fails I'll take it apart and clean it up.

Also the boot #2 that looks misshapen, is not on inspection. It must just be how the picture turned out.

I was as careful as possible with the tank and tried not to kink anything.

Lastly, "fun" is not the first term I would use to describe my experience so far. I'd rather be driving it in the warm air than fixing it in the snow!

[steves]

Those intake boots don't look right. I'm willing to bet they are ready for replacement.

[theman4444]

Those intake boots don't look right. I'm willing to bet they are ready for replacement.

You may be right about them getting replaced... eventually. I'm not sure they are on their last legs just yet. But right now I just want to make sure it will run period. I know that a bad intake boot can cause small problems after warming up but I don't see any cracks and they appear to make good contact so I doubt they are causing the issue where it TOTALLY dies and will not start at all.

I'm focusing my time, efforts, and money into the things that will definitely get it back on the road, and after getting her running I will do regular maintenance things. I may have to purchase a whole new electrical setup with spark plugs, wires, and coils so I'm holding back on possible unnecessary upgrades.

[Badfaerie]

You may be right about them getting replaced... eventually. I'm not sure they are on their last legs just yet. But right now I just want to make sure it will run period. I know that a bad intake boot can cause small problems after warming up but I don't see any cracks and they appear to make good contact so I doubt they are causing the issue where it TOTALLY dies and will not start at all.

I'm focusing my time, efforts, and money into the things that will definitely get it back on the road, and after getting her running I will do regular maintenance things. I may have to purchase a whole new electrical setup with spark plugs, wires, and coils so I'm holding back on possible unnecessary upgrades.

Just an aside, it sounds like you might have a small air leak, the main culprit of those are the intake boots. But there is a way to test that once you can work on it while it is a touch warmer. The o-ring that is between the intake boots and the motor is notorious for going bad so you will want to expect to replace those anyway. If the o-rings are bad you will develop an air leak as it warms up.

The air leak shows up as a hanging idle or a high idle that you can't adjust down with the idle adjustment.

It might not be a bad idea as well to re-sync your carbs since you've hand them on and off and stuff. (you'll need the bike warm to do this too) Home made manometers can be made for under $10 and work adequately for this.