Date: 01-06-20  Time: 00:22 AM

Author Topic: Carb Headscratcher...  (Read 2958 times)

Olly

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Carb Headscratcher...
« on: 12 May 2015, 11:31:52 PM »
Been riding my bike on a long commute since January (700 miles a week) and I've noticed my carbs have been getting progressively worse. The normal grumble between 6 -7k rpm now starts at 5k and starts to clear at 8 with a strong vibration through the frame.

Finally got round to a balance. Connected up the manometer started the bike and at idle no1 is sitting about right and the other 3 are all reading max on the gauges. Trying to adjust 1 increases rpm off idle; trying to adjust the other three stalls the engine due to low rpm.

Normally I'd say there was a leak on no1 but we've sprayed everywhere and there's no sign of any leaks at all. All the carb rubbers are less than a year old and were changed when the carbs were stripped, ultrasonically cleaned and rebuilt. Balancer hoses are a good fit with no leaks.

Anyone come across this before and offer any hints/clues at how to go on?

Only thing not standard on the bike that could affect this is possibly the exhaust. I've got a stainless exhaust from Sandyparts which doesn't have the balance pipes on the off-takes.
« Last Edit: 12 May 2015, 11:41:29 PM by Olly »

His Dudeness

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Re: Carb Headscratcher...
« Reply #1 on: 13 May 2015, 05:57:28 AM »
It could be a problem with the gauges. Try hooking up gauge 1 on the other cylinders one at a time and see if it gives a better reading. What type of gauges are they? Have they got restrict its in them?

Olly

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Re: Carb Headscratcher...
« Reply #2 on: 13 May 2015, 06:13:03 AM »
It's a friends Balancer so I'll need to check...

I didn't notice any restrictors. Here's hoping on an easy fix  :lol

Fazerider

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Re: Carb Headscratcher...
« Reply #3 on: 13 May 2015, 07:21:44 AM »

The aftermarket exhaust shouldn't be a problem, my fazer ran OK on the Sandybikespares downpipes and exhaust.


It is possible to get yourself in a tangle when balancing carbs if you try to do them in the wrong order. Match them in pairs: 1&2 then 3&4, then balance the left pair to the right pair. It requires a bit of alteration to the idle screw, once they're matched the revs will usually be a bit high so tweak it down and then adjust the balance again.


Once you've done all that, the throttle position sensor will need a check.
The "balancer" hoses are for the heater system to prevent carb icing.

His Dudeness

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Re: Carb Headscratcher...
« Reply #4 on: 13 May 2015, 09:50:18 AM »
A hesitation from 5000 to 8000 is fairly significant. I'd say a balance may help but a carb clean is probably in order. What mileage is on the bike? Must be pretty high if you're doing 700 a week. To get it running right you need to get all the basics right. So clean carbs and balanced, clean air filter, oil and filter, fuel filter, good chain at the right tension and sprockets, clutch cable lubed and adjusted correctly, bearings greased, gear change mechanism clean and lubed, good tyres at the right pressure, brakes cleaned. You could inspect the spark plugs and caps too and trim a few mm off the ht leads. Do all that and you'll be sorted :lol
« Last Edit: 13 May 2015, 10:00:08 AM by His Dudeness »

Jules-C

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Re: Carb Headscratcher...
« Reply #5 on: 13 May 2015, 12:26:21 PM »
At 5 to 8000 revs carb balance doesn't make much (if any) difference.  The carb needle will be controlling the fuel and the carb diaphragms controlling the throttle slides are very sensitive to small pressure differences from normal.  My first check would be new air filter if it not been replaced recently or cleaned if its a K&N

Olly

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Re: Carb Headscratcher...
« Reply #6 on: 13 May 2015, 10:22:27 PM »
It could be a problem with the gauges. Try hooking up gauge 1 on the other cylinders one at a time and see if it gives a better reading. What type of gauges are they? Have they got restrict its in them?

It's a mercury manometer rather than gauges or the digital type. No restrictors.

 :(

Olly

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Re: Carb Headscratcher...
« Reply #7 on: 13 May 2015, 10:40:13 PM »
A hesitation from 5000 to 8000 is fairly significant. I'd say a balance may help but a carb clean is probably in order. What mileage is on the bike? Must be pretty high if you're doing 700 a week. To get it running right you need to get all the basics right. So clean carbs and balanced, clean air filter, oil and filter, fuel filter, good chain at the right tension and sprockets, clutch cable lubed and adjusted correctly, bearings greased, gear change mechanism clean and lubed, good tyres at the right pressure, brakes cleaned. You could inspect the spark plugs and caps too and trim a few mm off the ht leads. Do all that and you'll be sorted :lol

I ultrasonically cleaned the carbs last autumn and replaced the rubbers,
New air, oil and fuel filters fitted at the end of last month,
Chain is fitted with a scottoiler and tension checked every week - I keep it at 35mm. Replaced at end of march along with the sprockets after the last one snapped at 110. That was interesting...
I stripped the bike for a deep clean 2 weekends ago, now they've stopped salting the roads, everything was re-lubed. I changed front and rear wheel bearings and put a new pilot road 4 on the back. Front has a road 3 with 3mm of tread left.
March was when I fitted the stainless exhaust. Put new plugs in at the same time.
Last weekend I changed out the metal and friction clutch plates and did the cable.

I've done 12k since the 5th Jan. Servicing the bike every 1 -2 weeks. Current mileage is only 23,800 (ish).

Haven't seen this problem before. Need to take my time and go through this one thing at a time. Problem is I'm running out of things to change - I've almost got a new bike..! Lol

bandit

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Re: Carb Headscratcher...
« Reply #8 on: 13 May 2015, 10:51:03 PM »
Carb balance first port of call, new end can wont affect running but K&N filter & definitely downpipes will, I have Motad downpipes with the balance pipes as many have on here but some have pipes without, mine refused to idle evenly until carbs were balanced. 

Silverlegacy

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Re: Carb Headscratcher...
« Reply #9 on: 15 May 2015, 01:59:21 PM »
the issues i have with my bike sound very similar to yours?
Although i did buy a carb tune and i sync'd the carbs and this made very little difference?
Im not sure when the carbs were last properly cleaned as i have only owned the bike about 8 months.


Jules-C

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Re: Carb Headscratcher...
« Reply #10 on: 15 May 2015, 02:32:30 PM »

It's a mercury manometer rather than gauges or the digital type. No restrictors.

 :(

My mercury ones have restrictors in the rubber hoses, small piece of plastic about 2 inches from one end of the tube.  Can't see anything but can feel them

His Dudeness

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Re: Carb Headscratcher...
« Reply #11 on: 16 May 2015, 11:19:16 AM »
You could do a plug chop. Hold it in the revs where its stuttering and hit the kill switch. Take the plugs out and see are they wet or dry and you'll know if it's leaning out or flooding. Don't let the revs drop