One thing is concerning me. The throttle plates, even with the idle speed screw backed completely off the linkage, are open far enough that the first hole of the progression circuit is exposed. Is that normal? If it's not, how do I fix it?

 

pm IOTUS on the forum, i gave him a ton of tech support and he got the dellorto to run much better.. using a good AFR gauge is key to proper tuning

 

yes, they are never spot on. you can tweak the throttle plates if you have a uni-synch otherwise don't mess with them

 

Ok need some help here guys. When I was rebuilding the carb today after cleaning, I was consulting this exploded diagram.



I noticed when I was taking the carb apart that two little ***** (#49) fell out. So when I was looking at this diagram, I noticed that I am missing #48 (pump jet spacer rod, sometimes referred to as pump jet weight i think?) as well as #51 (spring)

Are both of these pieces definitely essential? Or is there some reason mine might not have them?


Also, I read that it is essential for the pump jets to be facing a certain direction, but I'm not sure what direction that is and how to make them face that way after it's screwed in.

Edit: Researched some more. The spacer rod is apparently not part of the racing beat modified carbs. Neither is that spring.

However, I have found a problem. The hole drilled into pump jet housing (on the body of the carb) on one choke is misaligned. It's off center from where the actual pump jet's slot is when it's fitted into it's correct position. So therefore I don't believe much if any fuel is passing through this pump jet, which could be causing some of my hesitation issues. I'm not really sure what to do here. It's clearly a manufacturer defect on the carb body.

 

Took some photos. First and second is the good side, showing the hole drilled in the body lining up with the slot in the pump jet:




The third and fourth show the bad side with the misaligned hole in the body. How did this thing get through quality control?!




The best solution it would seem to be grinding another flat face on the pump jet so I can align it differently in it's housing. The holder can move around, so that's not too big of a deal.

 

I tested the pump jets, and despite the misalignment, they seem to work just fine. 2 solid streams shot out about 10ft for about 2 seconds.

I cleaned every passageway with compressed air and all of them were totally clear. Put new o-rings on all the jets and made sure all the jets themselves were totally clear. Put everything back together and....

It runs the same. Exactly the same. It's as if I had done nothing. Still running happily on one rotor and not a thing on the other. I took out both plugs and both plugs are pretty reasonable looking, although they did have a bit of gasoline smell and were wet. I just don't get it. I cannot find anything wrong with neither my jetting nor the carburetor itself, it seems to function just fine.

I tested my spark to each leading plug with a tester like this:



Each leading produced an orange spark inside the window, both about the same color.

 

Pull each plug individually and ground it on bare metal with the wire still attached and see if you get spark while cranking. Will take 2 people but good way to tell if its an ignition issue. It might start but shouldnt hurt anything. You could disconnect your fuel pump.

 

lol rb carbs ftw

 

So I tried something new today.

I started the car up from cold on a known unflooded engine. And it actually ran pretty well for a few moments before starting to act up again. I read that using an unlit propane torch and directing the gas into the throttles can help you roughly determine your a/f mixture. So I did that. With the engine sort of running, I held the torch up to each throttle and listened for a decrease or increase in RPM/smoothness. In both throttles the RPM's went down, which tells me that it's already got enough or too much fuel, so my vacuum leak idea is no good.

I can't help but feel the problem is due to the carb's first progression hole exposed when the throttle plates are 'closed' and I feel like whoever owned the carb before me gave up on it trying to figure out the problem, hence the reason it had .52 (!!) idle jets, which should be far too lean.

What do you guys think about plugging the first hole of the progression circuit and seeing if it helps?

 

Update:

On a hunch I swapped all of the ignition leads, deflooded and against everything logical, put the .52 idle jets back in.

It now runs much, much better. Holds a reasonably steady idle and revs cleanly with no load. I'm gonna try to get it out on the road and see how it does. I still don't get why it needs such lean idle jets to run properly. I do have them like 5 turns out, but still. It basically won't run at all on the .65 or .70 jets. It's almost like they're for a different kind of carb.

I do think part of the problem was the ignition leads, so I'm going to order a whole new set. Any advice on which ones to get?

My guess is that the ignition leads (unknown age) are simply not transferring enough energy to the plugs to ignite the fatter a/f ratio that the .65 and .70 jets are dumping in the engine. The .52 jets is much leaner so the spark doesn't need to be as strong.

Edit: I'm a complete newb at premixing and I put waaay too much oil (1/2 quart for not quite 4 gallons....a ~1:8 ratio...it should be 1:100) in, and as a result it's one hell of a smoke show. My neighbors hate me. Could this bugger up my a/f ratio in a way that makes sense?

 

Too late to edit:

If it is the ignition leads, that would explain why it had a lumpy idle even when it was fuel injected. I ordered a set of 10mm magnecor, as I've had good luck with them in the past (Merkur XR4Ti) and they are reasonably priced.

 

Despite the very lean idle jet, the car seems to be running pretty well. Took it for a drive this evening and it only has a couple little niggles. It bucked once at low RPM in first gear, but for the most part it ran pretty well. I could tell it was running a little hot at low RPM. My throttle linkage is wanting to hold the throttle plates open a little bit so I need to mess with that.

High RPM power seems very strong. It's throwing flames.

 

Youve just described carb performance in a nutshell. Youll find they run a lil different day to day depending on the conditions outside. The throttle return problem is an easy fix, just go to a larger return spring, or double up on them.

 

don't worry about the jet being lean, or rich, just look for the ones that make the car run the best.

 

Good to hear you got it running well.

The engine and running well with a 52 makes me think it's been drilled out, but hey, if it's running fine leave as is.

 

And the smile is the best part of all! Enjoy!

 

When I put the new wires on it, I'll possibly attempt to retune with .65 or .70 jets. We'll see. I'm just glad it's running solid.

 

try em, and you should try something smaller too

 

Well guys, after all that, bad news. I think I lost a seal.

I took the car for a drive this evening and after it was warmed up, I went for a second gear pull. It pulled strong and hard until about 6500rpm and then there was a loud ugly noise and I could hear that the car was only running on one rotor. No smoke behind, oil pressure didn't budge, coolant temp didn't budge, and it got me home, but it's making a pretty nasty sound when it's idling. Idles decently to be honest, but it has no power and the sound is horrible.

Is there anything else this could possibly be? I thought perhaps I had forgotten to tighten down one of the leading plugs and it had shot it out, but they are still fine.

Corner seal? Apex seal? Side seal? What do you guys think? And what would have caused it? The oil level is fine and my premix ratio was very oil rich.

Sadly, with grad school (half way across the country) looming and a lot of other things going on in my life, if the motor is blown I'm going to have to mothball the project for a few years. I was really looking forward to driving the car more with this setup too. Only got to drive it a few times...

 

It's pulling 10 in-hg vacuum at idle, and bouncing down lower too. I think she's a gonner

 

Do the driveway compression test.

Pull one leading plug and crank the motor by hand, 19mm deep socket on the crank pully. You should hear a strong puff evenly spaced apart. If it wheezes its low compression. If it skips one theres a big problem. If you squirt WD-40 into the motor and compression increases, all is not lost.

Put plug back in and remove the other leading plug. repeat.

My motors liked 80 or 82 idle fuel jets with the dellorto, that fixes the throttle tip in problem, which is the progression circuit. Assuming your acceleration circuit is ok.

I've run a horribly rich motor to the point carbon buildup made compression seals stick. And have run way too much premix which does the same thing but much quickier. This may be your situation. Low vacuum cause compression seals are not sealing all the way. Decarbonized it with WD-40, carb cleaner, or Amsoil Power Foam and that fixed it and it's back to pulling hard to 8000rpm. No ****.

I bet the spark plugs are very black, sooty and smell of gas. If the plugs look like that, the rest of the combustion surfaces do too.