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Dual IDF Tuning - 36HPVW
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txoval
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PostPosted: Sat Feb 18, 2017 6:40 pm    Post subject: Dual IDF Tuning - 36HPVW Reply with quote

Here is the engine:
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1200cc 36hp, Okrasa dual port heads, Cam was cut to specs of Porsche Super 90, Vintage Speed Exhaust.

I had PM'd and emailed a few of you earlier when I was first having issues with carbs. Alfa corrected the progression hole on the one barrel and now the car is running on all cylinders. So now the tuning issue/questions. Mr. Tucker recommended throwing it out to the board.

Currently Dual Italian 36IDFs, 110 mains, F11, 180 airs, 50 idles.

Tried with 220 airs as well...no difference

Lean best idle found, timing set a 10*BTDC, 019 distributor, carbs are sync'd (at idle).

My issue is that just off of idle (idles great) to 25% throttle, both carbs will spit and the carbs sound like a "tweety bird" if that makes sense.

I tried my 42.5 idles with both 180 and 220, not much change...same issue.

Could it be the linkage? One issue I am having, and common with Vintage Speed, is that no one makes kits for anything. I had to take an Okrasa CSP linkage and modify it to fit the IDFs. The connecting arms are not ideal, but from my eye, they open at the same time.

I tried a CB hex bar setup, but I had to modify the heck out it to fit the narrow 36hp engine and could not get full throttle or even close.

I hope someone can offer so help, at idle and 50%-100% throttle it runs great.

Thanks
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carock
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PostPosted: Sat Feb 18, 2017 7:25 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

How are you synchronizing the carbs? Do you have a real synch tool or are you doing it by ear? One possible problem is that you have a carb or a single throat in a carb that is way out of synch. If a single throat is out, then you usually have a bent throttle shaft on that carb.
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txoval
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PostPosted: Sat Feb 18, 2017 7:31 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Using a German SK meter...all 4 throats are the same at idle
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PostPosted: Sat Feb 18, 2017 7:35 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

If the carbs are opening equally, and they are 100% sync'd, try upping the idle jet some. Too small an idle will cause a stumble right before it transitions into the main circuit.
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txoval
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PostPosted: Sat Feb 18, 2017 8:00 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

My fear is that orientation of the linkage arms is causing a slight difference, but changing idle jets is a lot cheaper than buying another linkage.

The only linkage that will probably work is the Sync-Link version made/sold by another Samba member. The Berg linkage is too wide as well.

So obviously 42.5 idles are too small...50's did work better, what size should I shoot for?

Forgot to mention I have 27mm vents...should I change to F15's?
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PostPosted: Sat Feb 18, 2017 8:43 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Not real familiar with the 36 IDF's on vents, or emulsion tubes. I've played with 40's with the standard F11's, and 28 vents on 1600's, but nothing smaller like a 1200. I don't think the tubes will make much of a change in the lower rpm range. I would leave what you have, and try a 52.5 idle.
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Mikedrevguy
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PostPosted: Sat Feb 18, 2017 8:50 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

I see what you mean about the linkage maybe not allowing carbs to open evenly. If that is an issue, won't that still be an issue regardless of what jetsam Eusebio?
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modok
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PostPosted: Sat Feb 18, 2017 9:15 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

I would have started with 57 idles

The idle system is just like dellorto drla, and tends to use the same size idle jets as if they were dells.

OR

if these are the ones where alfa1750 on ebay has modified the transfer ports, then that will not apply, and I shall recommend you take them off, and instead source some different 36 IDFs that have not been ruined. Yes ruined.
You don't see anybody modifying Dells to have LESS transfer ports, and charge MONEY for it? Lets put in some totally wrong CB performance vents too to complete the massacre. I had NO problems making the carbs run SUPERIOR to universal models with no special changes at all, and it was BETTER before the internet, there was no misinformation to make you chase your tail and buy the whole jet kit running what a whole committee advises.
Read the WEBER manual, the one translated from Italian, and basic methods. The idle up procedure should have made it clear to see the idle jets were off before driving, although I will say, it is amazing how well they do run with one size too small.
sorry for the rant, if it does not apply to you.


Last edited by modok on Sat Feb 18, 2017 9:37 pm; edited 1 time in total
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txoval
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PostPosted: Sat Feb 18, 2017 9:30 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Modok:

Definitely need more data here, as the progression ports have been a major issue for me with Alfa. There are only 4 progression holes and yes, Alfa removed the originals and installed these "plugs" with new holes drilled.

If I'm reading your post correctly, I'm pretty much screwed. If so, I'll just move forward with a new set of Spanish 40's
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modok
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PostPosted: Sat Feb 18, 2017 9:38 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

I'm sorry.
Crying or Very sad

Yes get some different carbs and see how things go. Not good to jump to conclusions like I do.
If what I assumed is true, might want to tell alfa1750 needs to quit doing this, once you are sure.

I think the alfa1750 I knew 15 years ago, is now a different person, or persons.


Last edited by modok on Sat Feb 18, 2017 9:46 pm; edited 1 time in total
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txoval
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PostPosted: Sat Feb 18, 2017 9:46 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Any idea why he does it in the first place?

Should I try the 57's just to check? I hate throwing away $600
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Danwvw
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PostPosted: Sat Feb 18, 2017 10:01 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

What a beautiful set up! Love the 36Horse case with the carbs on it! Makes me want one! Not sure what is going on with your carbs but is there a way to adjust the overall full throttle adjustment so they open all the way together?

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modok
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PostPosted: Sat Feb 18, 2017 10:03 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

It is certainly possible to fix whatever the problem is, and it might be possible to make them better than they ever were, but I think the testing should be done on common old engine you know well.

You should get some known good carbs on there and see what it can do!
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PostPosted: Sat Feb 18, 2017 11:50 pm    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

36 DRLA...

$.02
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PostPosted: Sun Feb 19, 2017 1:41 am    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Has Alfa modified the idle air at all to match the modified transition ports? The reason I ask is I have had to solder and redrill a set on a 1600 that ran f11 tubes but that was with the original progression holes
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PostPosted: Sun Feb 19, 2017 2:56 am    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Unmolested $175 per pair
http://www.ebay.com/itm/Weber-36mm-idf-carburetors...mp;vxp=mtr

Yes you can try larger idle jets. It might work great, might not.
I don't know. I don't know what will happen, only can guess.
You can be sure nobody has ever assembled that particular combination before. Being small cc, I think 36 IDFs or 36 or 40 DRLA would be better choice than common 40 IDFs, as they have more transfer ports (or, they are supposed to anyhow)

Running 27 vents at 1200cc is like using 32 on 1600cc
32 vents on a 1600 is not going to work with common 40 idfs, but it could be made to work with 44idfs or 40 dells. you need more transfer ports and idle jet to carry the engine until you have enough flow to kick in those "big" Wink 27mm vents

if there is no sign the idle jets are too big, then keep going up until you find out where too big begins
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txoval
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PostPosted: Sun Feb 19, 2017 6:25 am    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Thank you for all of the responses. Alfa did not modify the idle airs.

There are a few people out there running this setup, but mainly with 36DRLA's.

I will go up on the idle jets first.

Would buying a pair of the original 36IDFs and swapping the good parts from mine be an option? Who in the US would do this? I assume Blackline?

Glen, would you be willing?

Thanks again, I'll try bigger idles and report back
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oprn
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PostPosted: Sun Feb 19, 2017 6:41 am    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

Maybe it's the camera angle but I am not liking what I see with that linkage. I can't imagine it being very linear. The right hand carb looks like a 90 degree angle between the rod and the throttle arm were the left one appears to be at least a 45 degree angle. If this is the case carb balance will change drastically at different throttle positions.
Another tip off to me is that at idle and full throttle it runs ok.

Others with more experience would know better than me though.
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Brian_e
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PostPosted: Sun Feb 19, 2017 7:11 am    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

I would also double check your linkage. It looks like the throttle shaft arms might be different lengths and at different angles. The small carb arms need to be the exact same length from the centerline of the shaft, out to the center line of the rod end. They also need to be at a similar angle so they rotate the same amount once the rod is attached. Once you get that set, the side to side linkage rods need to be parallel or at least similar angles. If one is flat, and the ofher at a big angle, they will not follow the same arc path, and they will be opening at different rates.

The center bellcrank also needs to rotate correctly. This is just an example, but at idle, the line from the bellcrank pivot through the linkage rod bolt hole should point at the left front tire, and at WFO it should point at the right front tire. If it points straight ahead at idle, and 90deg to the right at WFO it will be pulling the two rods differently throughout the range.

Getting them synced at idle is easy. Getting it synced through the rest of the range is the hard part.

Easy to check....without the car running, open the throttle all the way up. Look down the barrels and see if they both appear to be open the same amount. Do the same at mid throttle.

I have always preferred the CB linkage. I think it is easier to set up correctly, and has fewer potential geometry issues.
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txoval
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PostPosted: Sun Feb 19, 2017 7:25 am    Post subject: Re: Dual IDF Tuning - 36HPVW Reply with quote

The linkage arms on the throttle shafts are the same length, but opposite angle due to the "push/pull" linkage, left arm is on top, right arm is below. The linkage rods (from center mount to carbs) are definitely not identical. It's impossible with one arm on top and the other on the bottom.

I may need to buy the CSP center mount for late style engines and simply swap the center (SS pipe and arms) to my bracket which only fits 36hp cases. The late model version in not push/pull...it's pushes each side as the mount points are opposite of each other, where mine are on the same side.

I have measured at 25% and full throttle and they are very close, can't see a difference with my eye.
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