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TR1 engine Carburation problem (Read 1534 times)
Gerryg
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TR1 engine Carburation problem
13.06.22 at 17:25:33
 
Hi
I'm a long term member but haven't been active for a while.
My TR1 engine has always had a flat spot just off idle.
The use of current fuel has made it horrible so I have changed the diaphragm's and tried shimming the needles to richen it up a bit.
Also l turned mixture screws out a turn or two. Are there any intermediate drillings which affect light throttle openings on Hitachi carbs?
It still idles and runs well above 1/4 throttle but not in between. I would be grateful if anyone has a cure for this low throttle flat spot.
Regards
Gerry
UK Bedfordshire.  

 
 

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hornschorsch
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Posts: 2557
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Bike: TR1, SR500, XJ650-Turbo, RD350-YPVS, R[DG]500
Re: TR1 engine Carburation problem
Reply #1 - 14.06.22 at 09:03:36
 
Hi, i believe you should clean the carbs and especially the idle jets. Use carburetor cleaner and/or ultrasonic.

 
 

Gruss,
Schorsch

Fahrt so schnell ihr könnt, so lange ihr noch könnt!
(Uli Peil im XJ-Forum)
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Gerryg
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Re: TR1 engine Carburation problem
Reply #2 - 14.06.22 at 18:34:55
 
Thanks for your reply. I have ultrasonic cleaned the carbs bur reading the forum I may have created a problem by putting on aftermarket K&N type a/cleaners and caused turbulence problems for the diaphragms. There's not really room under the petrol tank for anything else. I see that some Viragos have 50 pilot jets, p;us I could try 1 mm shims under the needle would that help ? I don't intend racing my special but just making it a bit smoother.
If not what kits are available for other carbs.
Thanks
Gerry

 
 

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Gerryg
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Posts: 8
Re: TR1 engine Carburation problem
Reply #3 - 04.07.22 at 09:34:55
 
Hi
Does anyone know of an air cleaner or intake air tube to reduce flutter of the carb needle and slide.
Thanks
Gerry

 
 

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shalesy
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Bike: TR1 - 1984
Re: TR1 engine Carburation problem
Reply #4 - 04.07.22 at 10:19:09
 
I use a CarbMate - https://tecmate.com/carbmate/ Had it for years. I find it works really wel.

What really helped me was ditching the plastic bush that slides between the carbs and keeps them opening evenly and used a small roller bearing.
See this thread: https://www.tr1.de/pages/forum.php?iQuery=num=1629641187

I got the bearings from ebay: https://www.ebay.de/itm/363360670610

 
 

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craybait
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Re: TR1 engine Carburation problem
Reply #5 - 05.07.22 at 00:01:35
 
Great advice, can you advise what actual size bearing is needed,the website sells. different sizes and I would like to purchase before removing the carbs again

 
 

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Gerryg
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Re: TR1 engine Carburation problem
Reply #6 - 05.07.22 at 18:25:21
 
On a previous item the bearing size was given as 16x8x5
but I have yet to do mine.

 
 

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Gerryg
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Re: TR1 engine Carburation problem
Reply #7 - 05.07.22 at 18:33:20
 
On a previous item it was suggested that slightly enlarging the vacuum holes in the bottom of the needle slide would reduce needle flutter.
I can't get my head around that. Surely the movement needs damping down but increasing the vacuum passage way would speed up the effects and frequency of slide flutter. I would have thought that reducing the holes would be the way to go.
Does anyone have experience of this modification.
Thanks
Gerry

 
 

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shalesy
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Re: TR1 engine Carburation problem
Reply #8 - 07.07.22 at 08:15:47
 
Quote from Gerryg on 05.07.22 at 18:25:21:
On a previous item the bearing size was given as 16x8x5


Yup: 8x16x5mm # MR688-2RS

 
 

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Gerryg
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Re: TR1 engine Carburation problem
Reply #9 - 08.07.22 at 16:13:25
 
I have been talking to a guy who ran Yamaha Race Bikes in the 80's, they used and tuned diaphragm type carbs.
He was supplied parts and build sheets direct from Yamaha and consequently he's one of the few people with good facts from the era.

To change needle slide responses (mixtures and oscillation problems).
They reduced the slides vacuum feed holes flow by placing split pins, of different sizes, in the holes to reduce vacuum flow.
Also they detailed restricting the outflow from the top of the diaphragm chambers to increase back pressure and reduce needle oscillation frequency.

Plus another mod he used was to put a balance pipe between the two carb adapters, as used on some British sports cars and vertical twin bikes,
I didn't think it would work on our V Twins as inlet valve overlap could destroy each cylinders vacuum.

My engine has standard cams and I have installed balance adapters and a connecting tube. NOTE. It does not have a standard exhaust or intake system. Plus it has the American supplied replacement diaphragms which don't damp as well as the originals.

It  seems to have smoothed out the engine and got rid of the flat spot created by needle slide oscillation. The slides rise slower and smoother.
I don't know if my mod will work for others but it gives thoughts for improvement and is cheaper than the Mikuni conversion.



 
 

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