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#79190 - 05/08/05 9:07 pm Mikuni Jetting for T100C ????  
Joined: Aug 2001
Posts: 319
LDBennett Offline
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LDBennett  Offline
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Joined: Aug 2001
Posts: 319
Hesperia, CA
It happened again. After spending $50 for a Vintage MX practice the stupid pilot jet bush clogged after about five laps. Of course I had no tools with me to un-clog it. So I lost the practice time. The bush is so hard to get at (deep in a hole) and takes about an 0.018 inch probe to clear it (which of course I didn't have with me). It's Mikuni time! With the Mikuni at least I can get to the jets.

Anyone got Mikuni jetting for a 1970 T100C stock motor (26mm carb stock). My later TR5T runs a 28 mm carb with the same compression ratio and the same cams, so I imagine if there is no 26 mm jetting available I could go for the 28 mm jeting but I really would prefer to stay with a 26mm carb for the low end torque.

Anyone had good luck with Sudco recomendations? Their BSA A65 twin carb jetting sucked.

LDBennett

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#79191 - 05/08/05 9:26 pm Re: Mikuni Jetting for T100C ????  
Joined: Aug 2001
Posts: 4,221
Gordon Gray Online sad
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Gordon Gray  Online Sad
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Joined: Aug 2001
Posts: 4,221
North Carolina
Quote:
Originally posted by LDBennett:
snip "the stupid pilot jet bush clogged after about five laps" snip "The bush is so hard to get at (deep in a hole) and takes about an 0.018 inch probe to clear it"
LDBennett
LD....please help me out here????????

If the pilot jet clogged....why couldn't you still ride ??? I thought once your on the throttle the pilot jet is out of the circut?

Now this couldn't have happened to one of your new Amals could it??? For some reason I was thinking that a new carb solved all carb problems???what the heck is clogging it anyway????

I still say a screw in jet is an option...yes maybe not the BEST position for the jet?????...even though I believe it works for the 2 smokes...but it's sure easier to get to.

Cheers.....Gordon in NC

#79192 - 05/09/05 12:42 pm Re: Mikuni Jetting for T100C ????  
Joined: Aug 2001
Posts: 319
LDBennett Offline
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LDBennett  Offline
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Joined: Aug 2001
Posts: 319
Hesperia, CA
gordon:

While flying into a rutted MX corner, the brakes full on, it is not a good idea to have a burble of power on the exit if the plan of execution of the corner includes powering out. The pilot circuit is very important in cases where you are on and off the throttle, like you are continuously in MX. On the road you are probably right. I could have easily ridden the bike home, blipping the throttle during stages of the trip that required idling. I think the "LAW" would have objected as the bike has no mufflers at all, no lighting, and no license for street operation. It is loud and illegal for street operation. But the idea was to ride the MX practice anyway.

This AMAL is five years old. The problem is that at my age my opportunities to ride are limited and even more so since my son quit competing in MX on a regular scheduled basis. So the bike has sat for 6 months. I started it at home and it showed signs of a mild case of this problem. I attemted to probe the jet but must of not been sucessful (deep hole where jet resides). It started kind of OK (first sign of a clogged jet is hard starting) and had a stumble in the idle (second sign of a clogged pilot jet). It was OK for a few laps then it became hard to start and had a major stumble out of turns and wanted to die on coast downs. I drain the gas from the tank after every ride but I must have left gas in the float bowl this time.

What is the clogging agent? Who knows? I run race gas which should minimise the problem but the gas tank is fiberglass and it may be a product of dissolving fiberglass???? My Rickman Montessa has no such problem.

For a AMAL carb'ed bike ridden regularly this should never happen.

This clogging issue is not new. It has effected my MX days several times before and it took a bit to figure out what was happening. I'm just tied of fooling with it and I need a project. Mounting a Mikuni to this motor in the Rickman frame will be a challenge as the spaces are tight. I may even have to modify the intake manifold to gain enough room for the proper fit. But thats OK as my Smithy lathe/mill need a little activity as it has been "resting" too long as it is.

If I can not find good starting jetting for a 26 mm Mikuni I will abort the plan. I have no desire to spend my few outings on the MX track tuning a Mikuni to be able to even ride it. This is the same logic (ride rather than tune) that I apply to buying a new AMAL for Brit bikes of others.

LDBennett

#79193 - 05/09/05 1:23 pm Re: Mikuni Jetting for T100C ????  
Joined: Jun 2004
Posts: 1,115
kboyd Offline
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kboyd  Offline
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Posts: 1,115
Kansas
I was given info for dual carb 26mm Mikunis, if it helps to get you to a starting point...

The jet sizes on my pair of VM26's are as follows:
Main 120
Pilot 30
Slide 2.5
Needle 5F21 (I think)

For a single 28mm Mik:

throttle slide 2.5
>jet needle 5F21 clip on bottom groove
>needle jet 169 O-4169 O-4
>main jet 140
>pilot jet 35 <OK unless your mixture screw is more than 3 turns out,
then go to a 30>
>air jet <use a .5>
>needle valve & seat assembly 2.8 >

These are just setups I've seen come across this site and saved on my pc. Hope they help..

As for Sudco, they set up a 30mm Mikuni for the P.O. of my t100 and it idled great and the high revs were OK, but everywhere in between sucked. Folks have recommended to talk to Stan at Rocky Point Cycle for tried and true Mikuni settings for Brit twins.

If you do go this route, I'm sure you know space is very limited. Intake length suffers, so I've been curious about an angled single carb mount. Mainly to try to get away from that ultra thin pancake filter and maybe use a K&N. I'd like to try a t100 off roader someday.

Kyle


Kyle#44x

1969 T100R Daytona
1979 Powroll Honda XR250 "Dallas Baker" flattracker
1975 XL350 project bike
#79194 - 05/10/05 2:21 am Re: Mikuni Jetting for T100C ????  
Joined: Aug 2001
Posts: 4,221
Gordon Gray Online sad
Life Member
Gordon Gray  Online Sad
Life Member

Joined: Aug 2001
Posts: 4,221
North Carolina
LD....thanks for clearing that up for me. Makes sense that if your backing off all the way on the throttle the pilot might be back in the circut. Had no idea the bike sat for awhile...and was thinking that the clogging was the problem and not the carb..but your probably right...something
musta got left in there.

Not to steal your thread....but what kind of gearing (sprockets) do you use on your mxers??? I'm trying to set up a B40 for AHRMA's ISDT events and there's going to be a little MX involved.

Cheers and good luck with the Mics...the only one I've owned is on the Norton...so far it's been as reliable as a hammer.

Gordon in NC

#79195 - 05/10/05 12:05 pm Re: Mikuni Jetting for T100C ????  
Joined: Aug 2001
Posts: 319
LDBennett Offline
BritBike Forum member
LDBennett  Offline
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Joined: Aug 2001
Posts: 319
Hesperia, CA
gordon:

Poor throttle response will put you on the ground every time!

My Rickman is geared ideally for MX (thanks to Matt at Speed and Sport). It is geared for a top speed of 75 MPH at 7500 RPM with 17/60 sprockets. The front sprocket is cut down to 520 chain size by precision grinding (was 530) to gain a little chain clearance for rear tire and to be able to find rear sprocekts for it. Of course I run 520 chain.

Numbers for my twin don't translate well for your mild B40 single. There area a bunch of western AHRMA guys that race pre-1965 BSA singles and I am sure that they would have the gearing info you need. I'd try to find the AHRMA riders forum on the WEB and pose the question or go to a western AHRMA race and look for them in the pits.

LDBennett

#79196 - 05/11/05 12:04 am Re: Mikuni Jetting for T100C ????  
Joined: Nov 2004
Posts: 1,694
trumpetloon Offline
BritBike Forum member
trumpetloon  Offline
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Joined: Nov 2004
Posts: 1,694
georgia
LD "Baseline" jetting on any carb is dictated by your altitude, engine tuning specification and possibly the phase of the moon. BTW, my 500cc racing dirt track buddies (at altitude 17 feet) ALL run either 30 or 32mm VM roundslides.
Please do not cut that Rickman frame to install a carburetor. Sacriledge will bite you later. I used a 10 degree offset manifold to mount the VM I will use on the TR5T and only a small amount of grinding was required. Kboyd fought with this same carbie for awhile... my turn next.Go back to a repro AMAL if need be. bigt
Also BTW, if you still need a STD trans for your dual sporter... check out eBay auction 4548921021. Cheers... Mark


1974 TR5T
#79197 - 05/11/05 11:20 am Re: Mikuni Jetting for T100C ????  
Joined: Aug 2001
Posts: 319
LDBennett Offline
BritBike Forum member
LDBennett  Offline
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Joined: Aug 2001
Posts: 319
Hesperia, CA
trumpetloon:

Yea, I know about "baseline" jetting. I also know that Sudco jetting can be wrong, real wrong. I have spent years and years fooling with the dual Mikunis on my BSA Hornet and am still fooling with it (I am going to try Victory's approach to jetting this week).

I would never modify my Rickman frame to fit a carb! What would be needed is to modify the intake manifold by cutting and welding so that it ended in a round tube the same diameter as the carb and a bit shorter. Then use a correctly sized hose and a pair of hose clamps to secure the carb to the manifold. But the adapter to the air box would have to be shortened. I would be left with a stub just wide enough for a hose clamp. I think those mods would let the much longer Mikuni fit.

But I have yet to see real proven jetting for a 26 mm carb. This is a MX bike that need the 26 to have good throttle response. Big carbs like a 30mm, while working great at terminal speed, usually bog off an ilde and run poorly at small throttle openings on a little 500.

So until I see someone's developed jetting for a 26 mm Mikuni I'll not make the change. I cleaned the AMAL and of course it now idles perfectly. While not dirty inside that you could see, those tiny idle passages must have been clogged from varnish or who knows what. I added a fuel filter to the fuel supply line in case it is something from the tank. I also made up a probe I'll carry to the track from now on (Had one before but was mistakenly left in my truck when I sold it). And I'll not leave home without a can of carb spray!

LDBennett

#79198 - 05/12/05 4:09 pm Re: Mikuni Jetting for T100C ????  
Joined: Jan 2005
Posts: 429
gs750 Offline
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gs750  Offline
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Joined: Jan 2005
Posts: 429
New York
LDB, I contacted I don't know how many people, experienced vintage Triumph dealers and mechanics, last year on this very question. No one was able or willing to supply jetting specs for a 26mm Mikuni for use on a T100. Looks like we're both living with the AMAL until further notice.

gs750.


1971 Triumph T100C
1974 Honda XL350
1982 Suzuki GS750T
2000 Honda VFR800FI
#79199 - 05/13/05 11:51 am Re: Mikuni Jetting for T100C ????  
Joined: Aug 2001
Posts: 319
LDBennett Offline
BritBike Forum member
LDBennett  Offline
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Joined: Aug 2001
Posts: 319
Hesperia, CA
I am currently trying out the supposed correct jetting for my Hornet (mine was developed over about ten years and is OK but at the edge of too lean for sea level opertion but I live at 3000 ft.).

The first attemp went extremely poorly following "THE" procedure and initial jetting. I can not even get the engine to run cleanly sitting in the garage with the base jetting. So I'll try again, this time with the suggested richer needle jet and a bigger idle jet.

Jetting a bike is such a pain because it is dificult for me when the bike barely runs to determine if it is too rich or too lean. I'll give it one more day of effort and if that fails I'll write the exercise off and return to my jetting that works OK (and is "wrong").

I ceratinly do not want to go through this on my MX'er as riding time on the track is extremely limited and wasting it jetting is not fun at all.

LDBennett


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