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 Post subject: Ugh... hate to do this
PostPosted: Tue Aug 26, 2014 7:07 pm 
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To the on ramp
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Joined: Tue Aug 07, 2012 10:31 pm
Posts: 267
Location: Northern Vermont
Country: USA
Bikes owned: T500, GT380, GS400
So while I'm working on my Titan, I'm riding... let's say... an off-brand bike.

I was riding home from work, driving about 10 minutes and all of a sudden the
thing starts coughing, sputtering and back firing. I had just filled it up with gas
the day before. I had ridden it to work... fine. I had left work... fine. 10 minutes
later I'm limping along the side of the road. It idled fine, It would propel me
forward as long as I didn't rev too much above 2000 rpm. It was really, really
sudden. Luckily I was able to make it home (after pissing a few people off).

So I pulled apart the carb to make sure nothing was stuck in the float bowl. I checked
the battery connections to make sure they weren't loose. Checked the air filter
and there were no dead birds floating around in there. I plan on replacing the
plugs tomorrow but until then I wonder... Can bad gas be the cause? It starts easy,
runs and idles great, I just CAN'T rev past 2500 rpm. I put in a little gas treatment,
let it sit and it seemed to be better but there was still a trace of the loss of power,
sputtering and backfiring.

Normally I wouldn't be too worried but I'm leaving on a 3 day bike trek (the Gypsy Run
in NY and NJ in the middle of September) and I've NEVER had any trouble with this bike.

Any ideas?

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Slow and steady may win the race, but without loud and fast it's just a waste


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PostPosted: Wed Aug 27, 2014 1:38 am 
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Road race school

Joined: Tue Feb 19, 2013 2:45 am
Posts: 839
Location: Sydney New South Wales
Country: Australia
Bikes owned: Suzuki GT750A 1976
Hi,two stroke,four stroke,diesel ?? might help to know what we are dealing with ? Sounds like fuel,as you say you filled up then had the trouble ! :?
Cheers,
Roger

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PostPosted: Wed Aug 27, 2014 4:01 am 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3255
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
Single carb. Might you be talking about a Harley?

Maybe you have an ignition problem.
Dwell time decreases with rpm, so you might get a good spark only when the rpm is low.

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BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Wed Aug 27, 2014 11:32 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2157
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
Advance/retard stuck (points)?


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PostPosted: Wed Aug 27, 2014 12:15 pm 
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To the on ramp
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Joined: Tue Aug 07, 2012 10:31 pm
Posts: 267
Location: Northern Vermont
Country: USA
Bikes owned: T500, GT380, GS400
Yes, it's a Harley. Like I said, it's only my rider until I can get my Suzy on the road. So it is a single carb to a V-Twin
engine. I filled it the day before, rode it home. Woke up and rode it to work. Left work and started riding it home, about
half-way home it was just like someone pulled the rug out from under me. At first I thought I had to switch it to reserve
(before realizing I had just filled up. But it was that sort of feeling. Then it just started coughing and backfiring and
the needle would get up to 2,500 rpm then instantly drop to 2000 or 1800 and just cough and sputter. I was only able to
limp it home by keeping it under 2500 which meant up-shifting quite a bit, often much earlier than I normally would.

My father was suggesting that the gas I filled up with may have had water in it but it seems to me that it wouldn't happen a
day later and after I'd already gone 30 miles or so...

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PostPosted: Wed Aug 27, 2014 6:30 pm 
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Around the block

Joined: Tue Dec 25, 2012 4:43 pm
Posts: 97
Country: USA
Bikes owned: Honda-350, SUZUKI GT550 x2, GS850, 92 VMAX,
Can you tell if it is one or both cylinders? I usually tell by BRIEFLY touching a WET finger to the header pipes (don't let it burn ya!), but if ya have an IR thermometer, all the better! If it's fuel related with the single carb, both pipes should be about the same temp.
If it's ignition related, one will probably be cooler than the other.

Also, if you suspect bad gas, why not just drain it out & try some new gas from a trusted source? It's cheap, quick, & easy to do (a rare combination!). But run it for a while with the new stuff to be sure you've flushed all the old out of the system.

Could be a clogged filter, either within the tank, or external, or another possibility may be the fuel cap is not venting properly to let gas out of the tank....Try running with the cap open for a while.

Good Luck.


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PostPosted: Wed Aug 27, 2014 8:40 pm 
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To the on ramp
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Joined: Tue Aug 07, 2012 10:31 pm
Posts: 267
Location: Northern Vermont
Country: USA
Bikes owned: T500, GT380, GS400
Thanks all for the suggestions.

I changed the plugs (because they were due, not because I thought they were really the problem) and let the
fuel additive sit over night. I took it out for a spin today and there's no sign of the issue.

I'm confused about it being the fuel. If that were the case wouldn't it also idle roughly? The idle was just fine,
like it always is. I wonder if something small got through and was just clogging up one of the jets and the fuel
additive may have cleaned it out? Again, it was so sudden it doesn't make any sense.

Fingers crossed for the Gypsy Run, don't want to go through all that while out on the road. That gives me an
idea for a new thread.... :wink:

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PostPosted: Thu Aug 28, 2014 11:58 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2157
Location: The Republic of South Yorkshire
Country: England
Bikes owned: GT550s GT750 GSX1400 and lots of spares
Might have been a faulty plug. Are they resistor type? Could be a resistor breaking down as the revs rise or just a dud plug. Test resistance from top to centre electrode. Even possible that some carbon has built up inside.
Glad it's sorted even if it was a Hardly Ableson!!


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PostPosted: Thu Aug 28, 2014 12:19 pm 
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On the main road
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Joined: Mon Apr 21, 2014 6:09 am
Posts: 102
Location: North of Annapolis Md
Country: USA
Bikes owned: none
It doesn't happen to have the Delphi fuel injection does it? It sure sounds like one I troubleshot a while back....

If so, you might have your hands full without the proper equip.

jeff

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Present: VStrom 1000 K7, Stock: '74 RD350,’75 GT550,'76 CB400F, '75 H2(purple), Modded: ‘75 GT550 restored & ported, '82 Yamaha 650Turbo running 18PSI,'74 H2B carbs-pipes-ported, project list:'72 & 2-'75 H1's, '82 Yamaha XV920, 74 GT750


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PostPosted: Sat Aug 30, 2014 3:49 pm 
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On the street

Joined: Sun Mar 10, 2013 3:42 pm
Posts: 37
Location: South Jersey
Country: United States
Bikes owned: GT380 X 2 / GT500
Check gas caps, could simply be vapor lock. Seen it more then once on many Vtwins. From your description it seems like fuel problem.

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1972 GT380 x 2
1976 GT500
2000 Indian Chief
2003 Indian Scout Deluxe


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PostPosted: Tue Sep 02, 2014 9:33 am 
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To the on ramp
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Joined: Tue Aug 07, 2012 10:31 pm
Posts: 267
Location: Northern Vermont
Country: USA
Bikes owned: T500, GT380, GS400
well... turns out it's not sorted. I guess I'm going to drain the tank and see what's going on. In the meantime I've learned that, when it happens, all I have to do is up-shift way too early, let the bike bog down, pick up some speed, get the rpms up and when it starts to buck and shudder again I just up shift again and keep going until I run out of gears.

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Slow and steady may win the race, but without loud and fast it's just a waste


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PostPosted: Mon Sep 08, 2014 8:43 am 
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To the on ramp
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Joined: Tue Aug 07, 2012 10:31 pm
Posts: 267
Location: Northern Vermont
Country: USA
Bikes owned: T500, GT380, GS400
Replaced the coils, no good. It's definitely happening when the bike heats up to a certain temp as
it runs beautifully for the first 10 minutes then gives up the ghost after that. Methinks my trip is off... :cry:

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Slow and steady may win the race, but without loud and fast it's just a waste


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PostPosted: Mon Sep 08, 2014 8:02 pm 
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Joined: Sun Dec 14, 2008 9:34 am
Posts: 474
Location: Whitby, Ontario
Country: Canada
Bikes owned: Original owner GT550L
Check the simple things first. Water in the fuel, fuel supply, clogged/restricted fuel filter or screen, vacuum leak to the petcock, water in the float bowl.


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PostPosted: Tue Sep 09, 2014 4:49 am 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3255
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
You could use an induction timing light to see if you still get a spark when the motor is hot.

_________________
BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Tue Sep 09, 2014 7:30 pm 
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To the on ramp
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Joined: Tue Aug 07, 2012 10:31 pm
Posts: 267
Location: Northern Vermont
Country: USA
Bikes owned: T500, GT380, GS400
As it turns out, the Ignition Module is heating up too much and cutting out, funny since it's located in
the engine just above the exhaust pipe :shock:

The part is back ordered across the country so ordered an aftermarket replacement and am having it shipped
overnight to me. I'll have to retrofit the wiring but I think I'm good for it... trip may be back on...

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Slow and steady may win the race, but without loud and fast it's just a waste


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