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Carbs

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Re: Carbs
#31
ceecpa Avatar
ceecpa Silver Member Charles Edwards
Richmond, Virginia, USA   USA
I've not changed to Mikunis yet because cash has been demanded by other needs. It's still a dream.

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Re: Carbs
#32
JimG Avatar
JimG Jim G
Aurora, CO, USA   USA
Rick,
Can you describe the issue your havving ? does it stumble at throttke opening, does it go flat at higher RPM, flat spot in the midrange ?
jim

Re: Carbs
#33
RickR Avatar
RickR Rick R
Fishing Point, NSW, Australia   AUS
Hi Jim
Yes! she stumbles at throttle opening, I have tried several adjustments of the circlip up & down also different main jets.
Thanks for your interest.
Rick

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Re: Carbs
#34
JimG Avatar
JimG Jim G
Aurora, CO, USA   USA
Rick,
If it stumbles upon opening the throttle it's not in the needle size, clip position or the main. The stumble is likely the accelerator pump.
It's either not functioning properly or it's sending too much fuel. The accelerator pump is tuned in two ways, the pump jet size and the point it actually engages. I never had to change the pump jet size from standard but did fiddle a bit with the engagement point.My pump engages now almost immediately.
The other thing I wonder is about your fuel pump and fuel pressure. You have to regulate the pressure to about 3lbs of fuel pressure.
If you have too much pressure it could be pushing fuel past the needle valves just a bit and loading up on you when your off throttle.
What fuel pump do you use and is it regulated?
Below are links to a good tuning article and the Mikuni tuning manual.
jim


http://xlforum.net/vbportal/forums/archive/index.php/t-14060.html

http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf

Re: Carbs
#35
RickR Avatar
RickR Rick R
Fishing Point, NSW, Australia   AUS
Jim,
My current pump is unregulated, stock mechanical.
I will inquire about appropriate regulator & gauge.
Thanks for your advice, will update when I have tried your suggestions.
Rick

Re: Carbs
#36
Geko Avatar
Geko Stef SG
Kuala Lumpur, WP, Malaysia   MYS
It seems that many are interested in the Mikuni conversion but so far I've only read about Jim's experience with a RACING car. I'd be interested to hear more about the added performance for a road car even with a fast road setup (say below 130HP). Obvious reasons for Mikunizing would be tuning and consumption but I'm a bit doubtful about whether Mikunis would add anything in terms of performance as compared to stock carbs alone for a road car ?

Re: Carbs
#37
JimG Avatar
JimG Jim G
Aurora, CO, USA   USA
The Mikuni's were designed as a direct replacement for SU's. I switched to them based upon testimonials from street car owners.
Feel free to read other opinions from street car users.

http://www.v-performance.com/products/air_fuel.html

Rick,
I don't know what the stock pump generates for pressure but since it was designed to use unregulated with SU's & ZS carbs it's not likely your
overpressurizing the needle valves. Try going back to the Y6 needle, 195 main, standard pilot jet and work with the accelerator pump
adjustments. One more thing, when you look down the throat of the carb you can see the fuel spray from the pump jet. That jet needs to be manually aligned so it sprays right past the needle. A pair of needle nose pliers turns it easily.
jim

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Re: Carbs
#38
RickR Avatar
RickR Rick R
Fishing Point, NSW, Australia   AUS
Jim,
Thanks again for your help.
I have changed back to main 195, needle Y6, pilot 22.5, I am not shore if the 22.5 pilot is standard, I also have 20,& 25 pilot jets. Jet needle 97 circlip in middle.
I have adjusted the activation of the pumps as they were not in unison, I have also adjusted the spray to hit the needle & splatter, is that correct or should it miss the needle & go straight into intake?
Car is performing much better but still have hesitation off idle.

Re: Carbs
#39
JimG Avatar
JimG Jim G
Aurora, CO, USA   USA
Rick,
At the moment all I can think of it's getting too much fuel from the accelerator-pump pulse but I have my doubts.
Often times what appears to be a carb problem turns out to be ignition. If I were to look for an ignition issue
I would look for timing advance, or a lack of advance.
Is the hesitation from a dead stop or while rolling when you get on the gas. If your at say a 2000 RPM cruise and you step in it does it hesitate or stumble then ?
jim

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Re: Carbs
#40
RickR Avatar
RickR Rick R
Fishing Point, NSW, Australia   AUS
Jim,
From stop to go is ok. When rolling (in appropriate gear) at 1500- 2000 rpm with foot off throttle if you increase throttle very slightly she jerks back & forth, however, if you depress throttle its ok.
I, like you, thought it was ignition advance problem but local mechanic says no its carbies, I think he is wrong.
Since your advice & my adjustments she is now going very well other than the above.
I have now booked her in to a recommended local dyno mechanic familiar with 4 cylinder classics to give her a tune & dyno next week.
I will update next week.
Rick

Re: Carbs
#41
redoakboo Dick Vinal
Clermont, , FL, USA   USA
1957 Triumph TR3 "Ruby"
Do you mean Webers? Never heard of a Wever

Re: Carbs
#42
andymccl Avatar
andymccl Andy McClung
LAWRENCEVILLE, Georgia, USA   USA
Mikuni on tr4a

Do you have to have electric fuel pump or will the stock one I have work with Mikuni's ??

Re: Carbs
#43
RickR Avatar
RickR Rick R
Fishing Point, NSW, Australia   AUS
Andy,

The standard mechanical pump works fine on mine with twin 45's

Re: Carbs
#44
A. Bradley Aaron Bradley
Erwin, TN, USA   USA
1969 Jaguar E-Type 2+2 "The Jag"
1975 Triumph TR6 "The TR"
Very pretty and cool. I don't know much about the TR4 engine but, 'just wondering your input on how these Mikuni 45's would work/perform on a healthy and mild TR6 engine...from city driving to auto crossing.

In reply to # 732951 by JimG The Mikuni HSR 45's are fantastic. They flow the same as the Weber DCOE 45's, have accelerator pumps and you can buy parts at any Harley shop. They were designed
as a direct replacement for SU's ot ZS's.
I picked up significant horsepower and they give a real kick in the pants coming off corners. Super easy to jet too.
Last I checked Pierce Manifolds had them for about $ 245.00 each and then you need the
rubber boot adapters and phonolic spacers. Mine bolted right on.
One of the single best things I've done for my car.

Re: Carbs
#45
oldbagpipe Avatar
oldbagpipe Alec B
Bellingham, WASHINGTON, USA   USA
I thought Jim went to Webbers on his car?

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