Topic: Bike bogged down today (solved)

[fmctm1sw]

After nearly 4000 miles of trouble free service, I'm unable to go past half throttle without bogging down.  I limped home at 50mph max.  Typically this results from me forgetting something under the seat and the air snorkel getting blocked.  No luck this time.  I removed the air filter completely, same thing.  Plugs looked good, so I brushed off what little blackening was on them, still no go.  Thought it might be a fuel delivery issue with the fuel cap so I opened it while riding, still no change.  Didn't hear any snapping from leaking coil wires either.  I guess tomorrow I'll look at 3000 mile tune up items, though I'm sure I did lot of that stuff within 3000 miles.  I just changed the oil and found an ethanol free gas pump and filled it last weekend...

[Gordon]

What bike?

Does it idle normally, and how does it run up to half throttle? 

Do all carb bowls have gas in them?

[fmctm1sw]

my '72 350F.  Yeah, idles great.  Everything great until 1/2 throttle.  I'll check the bowls tomorrow, didn't feel like getting covered in gas before supper.   I had my sediment bowl off last weekend too, it was spotless.     thanks..

[Gordon]

If you get covered in gas just from unscrewing the drain plugs from the bowls I'd like to see your technique sometime.

At this point there are a lot of things it could be, but one possibility that fits the symptoms is a clogged main jet in one of the carbs.  Did you ever use any kind of gasket sealer on the float bowl o-rings?  But let's wait and see what you find in the bowls first.

[fmctm1sw]

Well, here's the story.  The bowls all had gas in them.  #2 had just slightly less in it, all of the gas was clear.  The inside of the tank is spotless (lined two summers ago with POR 15) and the petcock bowl and screen were perfectly clear.  On the bowl overflows I had used plain aqarium tubing and it was hard and brittle and one even nearly 100% plugged with crud at the bottom.  I removed all of them and took a ride:  same thing.  Checked the timing:  spot on.  I ran a compression test as follows:

#1: 150 psi/ plug blackening
#2  155 psi/ plug perfect
#3  150 psi/ plug slightly blackening
#4  155 psi/ plug blackening

Now that I think about it, this bike is running exactly the way my '73 did before I went with smaller jets.  The top end on this bike has always been rather flat compared to my '73 but as long as it was running reasonably well, I just let it alone.  I typically don't go full throttle anyway.  Maybe it's time I called Sudco again and tried a set of 72s...

[Kong]

Well then, its the spark, isn't it?

[Gordon]

But you said the plugs looked good, and you cleaned off what little deposits were on them and there was no change.  An overly rich mixture would typically result in sooty black plugs, and cleaning them off would allow the engine to run better for at least a little while before the soot built back up. 

From reading your first post about the problem, it sounds like this happened suddenly.  Is that correct?  Or did it start slowly and get worse over time? 

Have you confirmed spark at all four plugs? 

[fmctm1sw]

I did check the spark yesterday.  Had it at all four plugs.  Idles great.  I'm going to wait until night time and check the wires to make sure nothing is amiss there but this only happens above 1/2 throttle.  I would say it was more sudden than gradual but like said, full throttle was never what is was on my other bike.  But you're right, I took the filter out yesterday and nothing changed. 

[Gordon]

I think it's either time for a plug chop with new plugs, or pull the carbs to see what's going on in there. 

You didn't say if you used a gasket sealer on the float bowl o-rings or not. 

[Spanner 1]

Here's my quess; # 1, #3, and #4 main jet nozzles have loosened and are partially unscrewed from their posts.... my 750A was running crappy one day and I opened the carb bowls to find #4 main jet nozzle lying in the bowl  ........... check and see if all 4 are turned 'home', not that obvious when you remove the bowls IMO. Check the slow jet nozzles too.... good luck 

[mlinder]

Had the same happen to me once. Same symptoms. Drop your bowls and see if yer jets are at the bottom of em.

[fmctm1sw]

You didn't say if you used a gasket sealer on the float bowl o-rings or not.  

Gordon, with two 350Fs it gets hard for me to remember   but I believe I had the perfectly round float bowl gaskets in the kit.  I think I would have had to use some kind of adhesive then, yes.  And the note about gas getting all over me... well gasoline and  flammable or otherwise caustic materials seem to be attracted to me    

Well, the winner may be Kong.  Check out this image sequence.  I never would have seen it in daylight and almost didn't see it with even with the "nighttime mode" on my camera.  My plug caps leaked a long time ago and I electrical taped them until I bought a new wire and cap set which I did oh, about a year and a half ago from Z1.  Forgot all about it.  And honestly, I can't remember what jets are in it other than they are 75s.  I know I had new gaskets but I may not have bought the main jets.  Meaning that o ring on the main jet may be hardened.  At any rate, I think I need the smaller jets too.  Thanks for the help!  I need to figure out how to do the wires because I've only had mixed success with the coil mod shown in the tips somewhere...

*edit* It's extremely hard to see.  The leak is shown in picture 2 and 4.  And I saw it on plugs 2 and 3 both.  Didn't even bother to look at 1/4, I figured two was plenty...

[Gordon]

Glad you found it!  Let's hope that solves the whole issue.

[fmctm1sw]

Glad you found it!  Let's hope that solves the whole issue.

I hope so, should find out today or tomorrow.  I figured the issue would be even worse when the bike is real hot and under load.  Like when I'm out on the road and not just revving in my driveway...

[fmctm1sw]

but one possibility that fits the symptoms is a clogged main jet in one of the carbs.  Did you ever use any kind of gasket sealer on the float bowl o-rings?  But let's wait and see what you find in the bowls first.

Looks like that's the winner.  I'll post some photos when I get home later today. 

[fmctm1sw]

Well, here's the story.  The bowl gaskets were, in fact, the shape formed ones.  But they were too big (see picture).  To resolve that, I used a sealant to make them hold their position in the bowl groove.  That sealant got in the bowl (of #1 mainly) and turned to slime.  It, in turn, clogged the main jet.  The jets were not new jets, so I surmise that o-ring on the main jet was letting fuel by as well.  I cleaned all the bowls, main jets, idle jets, and replaced that o-ring.  So now I have all clean jets and improved spark.  Should be a winner.  Planned on riding today but it's raining...  

*edit* ...and this time instead of the sealant, I cut a piece out of the gasket so it fits properly.  I risk a small leak but it's a close as I could get it.

[Gordon]

It's a good feeling when you finally figure out the problem.

Did you clear out all the sealant from the other three bowl gaskets?  The swelling o-ring is a common problem with aftermarket kits, unfortunately. 

Now go say five "Hail Soichiros" and pledge to never bring a tube of silicone near a sohc4 again.

[fmctm1sw]

Yeah, cleaned all the jets and bowls too.  The o-rings on the main jets was so hard and brittle, two of them literally cracked off.  And I had forgotten how much of a PITA it is to take the bowls off without removing the carb rack.   

[Kong]

Here is a rule that I learned a long time ago.  When all indications are that you have a fuel problem then the problem is probably in the ignition and anytime you are certain you have an ignition problem the culprit lies in the fuel system.

I did not, however, apply that rule when assessing the problem above.  I simply looked at what you had already done and came to the conclusion that first you had already done everything that was possible to do to the carbs and second was that if you were, as I assumed, a competent mechanic then the work was properly done.  So if the carbs were OK then all there was left was the ignition.  In truth I didn't for a second suspect your caps, I was going to place my bets on a stuck advance mechanism - they do stick and the effect if felt right about at 2000 RPM.  Just a thought if the problem persists or reappears.