Hesitation Under Load

[R65_Mark]

On last weekend’s trip to the North Georgia Mountain Rally (see here for some notes: Georgia Mountain Rally  I
had an occasional hesitation at 4,250 rpm or so on the Interstate stretches there/back (one up with lightweight camping gear on the back/in cases) if I really snapped open the throttle after a period of steady running.  It was mild, something less than “coughing” and it would not happen if I was a little less aggressive.  It might happen at other speeds after a period of steady throttle, but this the kind of speed “my” group was running and I did not do a lot of experimenting.  I’m really trying to ride this year rather than tinker, but if anyone has any thoughts, I’d like to hear them.  Mark

[Bob_Roller]

If you haven't been in the carbs lately, I'd do a quick look at the rubber diaphragms in the tops of the carbs.

Good chance there may be a tear in one.

[Justin B.]

I was thinking the same thing...

[R65_Mark]

Thanks for the thoughts.  OK.  I can convince myself that popping the tops off of the carbs is a simple job and a wise precaution that is prudent serviceability investigation and not just tinkering for the sake of it.  I should be able to find time this week (maybe even tomorrow) and will report findings.  Mark

[Crossrodes]

I have to tell you that I have had no experience with an R65 doing this...however I have experienced this in other cars and motorcycles.  The first thing I would check/replace is the fuel filter.  What you describe is a classic partially plugged filter.  

As the bike comes under load there is a demand for more gas which the system can't deliver because of the partially plugged filter.  Because the bike is starved for fuel the performance will drop off.

[Justin B.]

Or the gas cap is not venting.  Next time it does this crack the cap and see if the problem clears up after a short while...

[R65_Mark]

See, I knew this would end up in tinkering.  If the weather holds, I’ll take a 200-mile round “business” trip on the R65 this week and do some “live” experimenting.  Otherwise, next weekend I’ll (a) check the carb diaphragms, and (b) go through the fuel system and clean/check/replace filters depending upon what I find.

On a more “advanced” line of thought, my race car buddies suggest that now we seem to be getting fuel blends here in Atlanta with 10% ethanol the R65 might be running a little hotter, so a colder plug might be in order (say a NGK BP8ES vs. standard “7”.)  This will add (c) pull the plugs to take a look when I am doing the other things next weekend.  Any thoughts?  Also, any thoughts about Iridium type replacements?

Mark

[Bob_Roller]

I experimented with different plugs, mostly Bosch, with multiple electrodes and platinum core, and I saw no advantage in them, I am using the last of the Bosch plugs that I got a few years ago, and when they are gone, I'll be using NGK copper core plugs .

The platinum core plugs have a surface electrode, only part of the center electrode you can see is what is visible at the surface of the ceramic insulator, after 10,000 miles, there was  metal eroded away to a depth of about .070 in., so with a .030 in. gap setting, I had about .100 in. spark plug gap, and never noticed any real degradation of engine performance.

The high end plugs may make a difference in a high performance application, but personally wouldn't bother in the case of the R65.

We've had 10% ethanol in the fuel supply here for about 8 years, and the only thing I see different is a loss of fuel mileage, 4-5 mpg seems to be quite common in carburetor equipped vehicles .

[nhmaf]

I wouldn't try different cooler temp plugs unless you are seeing evidence of glazing or bits of molten electrode, etc.   Colder plugs just run with a colder "nose" but don't do anything to the combustion chamber temperature.   "Hotter" plugs just have a high thermal resistance between the center electrode and the body of the plug that contacts the cylinder head - the hotter temps are meant to facilitate burning off deposits around the electrode and center insulator.   For best service life, never run a hotter grade plug than necessary.

I agree that the ethanol addition (we are at about 10% in New Hampshire now also) generally reduces the average fuel consumption by about 5%-10% over what our automobiles used to do.  Still, I recall shopping for cars not that long ago and a Toyota Corolla could get up to 41 MPG (U.S) but now it seems they claim the fuel mileage is fantastic at 36 MPG.  I know that the ethanl could worst case account for this difference, plus the fact that the EPA changed their test loop for determining MPG.... but still it seems like we're going backwards in the MPG game

DO CHECK AND REPLACE YOUR FUEL LINES IN YOUR BIKE/LAWNMOWER/etc. more frequently with these 10% and above ethanol mixtures - until everything is replaced with either a vinyl or a rubber hose treated to resist the degrading effects of ethanol the inside of your rubber fuel lines are more likely to break down.

[Justin B.]

Aircraft Spruce just shipped my fuel line order today so after this weekend none of our bikes will have "rubber" lines anymore.  I'm going to use the polyurethane on a couple and the Bing alky resistant on the others...

[Bengt_Phorqs]

Justin, what size fuel line do you recommend?  Guess I'd better get started on swapping out on a few bikes.

[steve hawkins]

This is a common thing and we had a long thread about it recently.

Not sure if the 'victim' ever solved it.

If the bike picks up after the hesitation, then I feel it is unlikely to be a diaphram - if it was a diaphram failure then once you get to the 4250 rpm you would not go any further and it would continue to bog down.

If it was a fuel starvation issue, the symptoms would be similar - there would come a point when you could not accelerate any more and that would be it.

If you can accelerate through it, then you have a transient fueling issue with the main circuit which becomes an issue at a certain point and it just happens to be at highway cruising speed.  It is more likely to be running too rich at that point than running to lean possibly due to worn main jet/needle (How many miles has the bike done?) or it might even be due to changes in the fuel etc.

First you can try dropping the carb bowls and check for water or other bit and bobs (rust and rubber particles), neither of which will help your carburetters.  If you have never drained your tank now might be the time.

If that does not get any results, then get out there and reproduce the issue and get used to reproducing it, so you can always get it to happen.  Then lift the tops of your carbs, taking the opportunity of inspecting your diaphrams for even the tiniest of holes (just in case).  

Then I would lift the slides out and check the needle position is at the standard setting.  If they are, I would move them 1 click down to make it slightly leaner.  Put the bike back together, ensure that the carbs are balanced, and go ride it and see if it makes a difference.

If it cures it then great, but if you bike has any mileage on it, it might be time for a change of jets anyway.

Bike seem to be jetted differently in different markets, I know the bike in the UK are jetted differently to those in the USA.  So it would be worth getting a manual (Haynes, etc) and reading up on Bings.

[steve hawkins]

I have had both issues by the way,

Hesitation on my R65 cured by returning to standard jets and dropping 1 click on the Jet position.

What colour ar your plugs generally dark brown going black? - Too rich.  Light tan?  Just right.

On my R100, I had water and crud in my float bowls, forcing me to carry out a timely drain and flush of the fuel tank.

Both running fine now.

Cheers

[Ed Miller]

Try deliberately running the bike with the symptom happening, like Steve suggested, and do a plug chop as fast as you can to see if they are rich or lean.  Worn jets could easily do it.  

I had a similar weirdity some time back, and after a couple of years of false leads it turned out to be a defective carb body that was letting excess fuel past the needle jet.  I swapped all my jets into a different, used carb body and the problem went away.  The spark plug on that side was very dark when I checked it.  There's a thread about my issues somewhere around here.

[R65_Mark]

Thanks all for the continued input.

Did my planned 250 miles round trip over the past two days (bike has now just topped 23,000 miles).  I tried to replicate the problem on some of the longer-legged stretches without success.  However, this does not convince me the problem has “gone away” as I was mostly on State Highways/County Roads and never got to run at 55mph+ for any real length of time which is when the deal came up before.  Also, I was probably running 50lbs lighter than before (just a change of clothing and some notes for work in the hard cases - no camping gear).  Good thing is that I had a great trip (nice twisties in sunny and low 80’s/no rain weather).

I have the cleaning type jobs set up for the weekend, and will do some of the simple/basic carb checks as suggested, but I’m really trying to ride rather than tinker too much.  If I do not find anything obvious this weekend, I’m just going to ride and see if I can replicate the symptoms again.   The Huntsville, Alabama, Great Chicken Rally is two weekends away.  At 360 miles roundtrip, it’s a longer haul than I would normally do, but it might be a good opportunity to do some applied investigation/experimentation.

I’ll report back on what, if anything, my cleaning/inspection chores reveal weekend.

Mark