Weber MCHH carbs

[TomChar]

Hi all,

I recently bought a '74 TR6 with dual MCHH carbs. Car runs well, but it's definitely running rich. After quite a bit of searching the web, it appears that the MCHH is somewhat akin to half a DCOE, but I haven't found anything to actually verify that, or even found any techical docs specifically for this carb. I ordered a weber tuning book, that claims to cover the MCHH, but it hasn't arrived yet and the weekend's coming up .

Does anyone out there have specific info on these carbs, are the tuning procedures, jets, etc., the same as the DCOE?

Cheers,
Tom

 

[Mickey Richaud]

Welcome, Tom!

Just recently I read something about those. Not sure where it came from - maybe this forum...

Someone else will surely pop in here shortly with an answer.


Mickey

 

[hondo402000]

Be interesting to see what the book says, if its half a DCOE the good thing is you will only half to buy 1/2 the number of jets, but jetting is not as simple as going down one size, on the DCOE there are 3 circuits, the Idle circuit, the progression circuit and the main circuit and they over lap each other!

I wish you luck if its like jetting a DCOE, only took me 1 year after my engine rebuild to get mine running in the 13.1 to 14 range

by the time you get it right you will be a master of the carbs,

I would suggest you get a air fuel meter and install it so you know exactly where its running

innovate has a digital one, dont get the hand held units they suck

Hondo

 

[DNK]

...
I would suggest you get a air fuel meter and install it so you know exactly where its running

innovate has a digital one, dont get the hand held units they suck

Hondo

See
HERE

 

[TomChar]

Thanks guys,

In my searching I came across Redline, and sent their tech guys an email. I received a surprising quick and rather detailed response from them, describing the MCHH's as exactly that, half a DCOE. Alas, they are no longer in production, but are still serviceable.

With the info on their website and Bud's response, I've gotten the car to run much better, although not quite inline with the proper tuning specs. At this point I'm still tinkering a bit. A synchronizer is something he's recommended to help with tuning, although with only two venturis's, tuning *should* be much easier than with, say, you guys with triple DCOE's.

Tom

 

[hondo402000]

play with anything long enough and you get really good at it,

Hondo

 

[Lonestar245]

I recently purchased a TR6 with a pair of these MCHH carbs and they are in need of tuning. Running far too rich! Any help would be appreciated.

 

[poolboy]

I think I'll have your ZS carbs finished and shipped back later today, JD, if that's any consolation.
In the meantime see if your engine will tolerate a little ignition timing advance.
There's been times when the book's static and dynamic confused people resulting in incomplete combustion.

 

[TomChar]

I wouldn't say I had success, but it runs well enough for me. Something I've been toying with in my mind has been setting up an O2 sensor to measure the actual air/fuel ratio, but that's hasn't happened. I got great support from Bud at Redline, who's a supplier of Weber carbs. Essentially I found out that these are half of a DCOE. He sent me some docs which I can't attach - too large, but I can email them to you if you want. Both are pdf's.

I bought a tuning kit for a DCOE, that came with various jets, the more common sizes, from a seller on ebay. I bought a synchronizer for the carbs, and then needed to come up with a little PVC elbow fitting to point it away from the inner fender as it wouldn't fit over the weber inlets. Essentially I just took them apart and cleaned them. I didn't change the floats or anything like that, although Bud mentioned that there could be concerns with the ethanol in the newer fuels affecting non-brass floats.

Tom

 

[TomChar]

Just saw Ken's response regarding timing. One thing that initially had me confused is that these cars didn't come with a vacuum advance, but vacuum retard (at idle?) or some such. My car also came with the Petronix ignition kit, but when my tach drive gear on the dizzy wore out, I had it rebuilt back to the OE style points and have been happy with that.

 

[groupdeville]

I always wanted to come by a set of MCHH carbs for my TR2. Seems like a good balance between the complexity of a full set of DCOEs and the standard Triumph SUs or Strombergs. Maybe someday...
Too bad that the MCHH is out of production - from what I understand, they're also used on Harleys and other large-displacement bikes.

 

[poolboy]

At the 2014 6-Pack TRials one of our Canadian members drove his TR6 with the MCHH carbs down to the convention in Oxford Mississippi on the Ole Miss campus
He bought a pair of my rebuilt ZS carbs while he was there...He had never driven a TR6 with ZS carbs and I had never driven one with MCHH carbs.
We took turns driving each others cars...I couldn't tell the difference, but he seemed to think my car "pulled a little better" I think was his words.

 

[Lonestar245]

I think I'll have your ZS carbs finished and shipped back later today, JD, if that's any consolation.
In the meantime see if your engine will tolerate a little ignition timing advance.
There's been times when the book's static and dynamic confused people resulting in incomplete combustion.

Thanks Ken. In no way was this intended to rush you but thanks for the fast service! My objective with the ZS carbs is to hold them in reserve until I have convinced myself the MCHH's wont ever satisfy me, then swap them out. I suspect I am missing a number of parts to do the swap, but I haven't looked into that yet. I plan to do the research purchases while I am tinkering with the MCHH's so I will not be down any great length of time.

 

[Lonestar245]

I would appreciate it if you sent me the docs. It appears that in my profile there is a way to send them to my preferred email without me publishing it here in the open. Sounds like I need to find Bud at Redline as well.

I'm sure my car was run on pump gas in California and Arkansas after the rebuild. I am fortunate to have a few stations near me that offer ethanol-free fuel, so I am staying with that as much as possible.

 

[Lonestar245]

Just saw Ken's response regarding timing. One thing that initially had me confused is that these cars didn't come with a vacuum advance, but vacuum retard (at idle?) or some such. My car also came with the Petronix ignition kit, but when my tach drive gear on the dizzy wore out, I had it rebuilt back to the OE style points and have been happy with that.

This is the problem with buying someone else's Frankenstein. I can read about what parts were changed, but not how it was actually implemented. I have a Crane Cams Fireball electronic ignition and coil. The vacuum line (retard?) is disconnected, as it is supposed to be if I recall correctly when reading the install instructions for the ignition. I do have an old school timing light that I suppose I can relearn how to use it and check the timing. I did all that kind of stuff stuff in a previous life it seems now. Re-jetting carbs, ignition work, timing, etc.... It gives me tired head thinking about it now.

 

[Lonestar245]

At the 2014 6-Pack TRials one of our Canadian members drove his TR6 with the MCHH carbs down to the convention in Oxford Mississippi on the Ole Miss campus
He bought a pair of my rebuilt ZS carbs while he was there...He had never driven a TR6 with ZS carbs and I had never driven one with MCHH carbs.
We took turns driving each others cars...I couldn't tell the difference, but he seemed to think my car "pulled a little better" I think was his words.

I honestly would not be surprised, based on what I think I know about the carbs in question. Unfortunately, I am one of those people who "need to know" how things work, and if I can fix them, or make them work better. I just want to try to get tehse MCHHs running better if possible, before I make any changes.

 

[Lonestar245]

I always wanted to come by a set of MCHH carbs for my TR2. Seems like a good balance between the complexity of a full set of DCOEs and the standard Triumph SUs or Strombergs. Maybe someday...
Too bad that the MCHH is out of production - from what I understand, they're also used on Harleys and other large-displacement bikes.

From what I have read, they were designed for Harley's. Who would not want a Weber side draft on their show-n-go bike? I kind of feel the same about these on my Six. They have a 'cool" factor. But the question is, can they every be tuned to run properly in this car?

 

[poolboy]

I would say the answer to that is "yes" JD, based on the TR6 I drove with them.

 

[TomChar]

... I do have an old school timing light that I suppose I can relearn how to use it and check the timing...

As did I. Same with the brain. Dug it out of the ancient rusty toolbox buried in the corner of the garage when I bought the TR6, and upon first use it promptly fell apart. Same with the brain...

 

[poolboy]

You could just do a old school quickie check, by ear.
See if the rpms @ idle increase when you slowly rotate the distributor clockwise.
When it max's out back off a tad counterclockwise.