Timing chain question.

[Gregs672000]

Ok, after watching and hearing, I feel a little better, i.e. I didn't think "clearly a bent valve", so that's good. Still concerned, but more hopeful. 900 idle is fine and typical, a little lower is ok but not many U20s idle butter smooth at 600rpms. Joes write up is good. However he does not know you have an EI distributor in there, so ignore the dwell meter info, though very important for points dizzys. The rear or right side carb works as it should for air/fuel mix, but the front needs adjustment as noted. When you check, just push the pin up and hold. Once you get it closer it may shake less or stop. As the rings seat etc too it may balance out more.

Ignoring the unisyn for the moment, can you adjust the balance screw(s) to where the shake goes away? Watch to make sure the dog bones are allowing you to make adjustments. Turn your unisyn to where it reads on the lowest mark, that will help keep it from choking down the motor.

Since you are able to do video, once fully warm do one where you show idle, then slowly rev it up over about 20-30 seconds, slowly to about 3000-4000 rpms or so.

Again, a leak down test will give us a final answer on valves my friend... I'm hopeful! You may have dodged a bullet!

Nice car by the way.

[newby]

When you check, just push the pin up and hold. Once you get it closer it may shake less or stop. As the rings seat etc too it may balance out more.

Just to be clear how much do i push up? A little, A lot, all the way? Ive been pushing just enough for it stumble.

Since you are able to do video, once fully warm do one where you show idle, then slowly rev it up over about 20-30 seconds, slowly to about 3000-4000 rpms or so.
Again, a leak down test will give us a final answer on valves my friend... I'm hopeful! You may have dodged a bullet!

I had a long day at work so I wasn't able to get to much today. I will try again tomorrow.

Nice car by the way.

Thanks!!! I've worked really hard trying to get her here. Do you have more pictures of your roadster?

[Gregs672000]

Push the pin all the way up. I hear you on the work deal! I have some pics but they were on my old computer, and the ol hard drive gave up the ghost!

[newby]

OK sorry I took so long getting this but I have been sooooo busy lately.
Here is the video at idle:
" onclick="window.open(this.href);return false;
Here is the video of me pushing up on the pins on each carburetor and what it is doing.
" onclick="window.open(this.href);return false;
If anybody has any idea why it's doing that please chime in... ive tried adjusting the back carb all the way rich and all the way lean and it still does that to some degree.

[dbrick]

BTW, Joe is referring to Clockwise and counterclockwise looking down from the top, which makes a lot of sense vs. tighten/loosen. It is a right hand thread, but is pointing up. BTW All the carbs I've seen have a rivet on the knurled knob, good reference for how many turns.

[notoptoy]

Good videos, it is interesting when you push up on the back pin, it also seems to smooth out a bit. I would think that there is an ignition miss otherwise.
Have you tried removing spark plug wires, one cylinder at a time to see if you get any different results on one cylinder versus another?

[spyder]

Newby:

I have not messed with SU's in years but it looks like the rear carb is too rich and the front is too lean. Back in my SU days, the car ran fine but a reliable smooth idle was the hardest thing to get. I found that the pistons were worn and both did not rest at the same point at idle. Your carbs look very nice but I would check to see if the clearance is the same on both carbs pistons when down at idle. Mine weren't at idle and it acted like yours.

[Gregs672000]

In looking at the picture I realize that I don't recognize that carb linkage at all, so all the stuff I described earlier back probably makes little sense!

Anyway, 1) I'm not convinced the carbs are balanced. Please set the unisyn open more so it reads about 1/4 way when you test, that way you can slap it firmly on there and get a good reading then take it off without pulling down the motor too much. Forget the unisyn for a second; can you adjust the balance screws to where the engine does not rock like that? Can the linkage hold up any adjustments, like with the dog bones? Sorry but I've always had the solex set up so it's different.

2) I really need you to do a compression test... I need to know if we're wasting our time with carbs when we have a bent valve. That will help put that to rest, depending on what we find.

[spyder]

Another thought. Even if you have a cylinder firing weak, it smooths out at a higher rpm.

[newby]

2) I really need you to do a compression test... I need to know if we're wasting our time with carbs when we have a bent valve. That will help put that to rest, depending on what we find.

Greg I am going to try and do that compression test today. I have to find all the parts or run out a gets new one. It think it's a good idea to get that out if the way. What should my compression be? Or should I just worry that I get the same number on all 4?

[jrusso07]

You can rent or get a free loan of a leak down tester, possible a compression test gauge from local auto parts stores...just eave a deposit and that is refunded when you return the tool.

Compression values vary due to a number of factors but each cylinder should be with a few psi of each other like 5 psi or so. So think of it as a differnecenmeasure versus an absolute measure. Leak down tester is time to a psi value and gives you better insights into what might be causing low compression.

[jrusso07]

After watching vids, here are my thoughts. Both carbs are too rich.

Carbs look like they are newly rebuilt so I am going to assume three things are correct,1) needles properly seated in pistons, fuel bowl floats are properly set, jets are properly centered.

So, again, assuming above are true, turn both mixture screws CCW looking from top simultaneously until max rpm is found. Once found, turn throttle adjust screws to get back to 600 rpm (or whatever idle rpm you want). Balance with unisyn. As Greg said, hold the unisyn tight to the carb mouth. No Air to carb except thru the center of the unisyn.

Move mixture adjusts CW simultaneously to find max rpm. Reset throttle adjust screws to Desired idle. Balance with unisyn. Test mixture by lifting pins. When pin is lifted on first carb, idle will increase and then hold, same with second carb. If either carb causes the rpm to go higher and stay there, the opposite carb is too rich. If lifting pin causes rpm to drop or engine dies, other carb is too lean.

Once idle is set, go to high speed balance procedure.

I will email you my phone number if you want to talk through anything

Check out this book...it's about MG SUs so adjustments are different but concepts are the same. Look at p24. http://mgaguru.com/mgtech/books/pdf/Tun ... retors.pdf" onclick="window.open(this.href);return false;

[newby]

I was able to get a compression tester so I will do it tomorrow. Joe thanks for offering the help. If I get stumped I will give you a call.

[dbrick]

I need to have Joe set my carburetors. I only got it perfect once, and I think it was dumb luck.
I tried unisyns, but this kit really works for me. The 2 wires are pointers that rise with airflow and let you see the difference. It reads airflow using the carbs own pistons. and gives you a "handle" to lift the piston slightly to set mixture

from the forum photo came from.
.... If your linkages are sloppy, you can be in sync at idle, and nowhere else as the throttle opens up. This tool, as Peter says, allows you to see the sync as you go up the throttle opening range without having to continually readjust as you would for the UniSyn. That can tell you if you are truly sync'd throughout the rpm range and if your linkages are still in decent shape. This means fewer assumptions about what is actually happening.

For those who need a visual, here is what an SU Tool Kit in use should look like:

Been using mine since the mid 60s on H and HS carbs.

[Gregs672000]

Really good info and suggestions.

Since your motor is new and the rings may not have had time to seat etc, the actual number is not as important as they being all fairly close. In this case, I want to see if one or two cylinders are really different... Looking for that bent valve. As Joe said, a leak down test will show us exactly what's going on, but it is a bit more involved and requires a compressor, etc, so I thought we would start with compression and see what that shows us. Warm the engine to operating temp, then pull all the plugs, disconnect spark, install tester in number one, put the clutch in and open the throttles full (foot to the floor!) and crank the motor over 5-6 revs to pump up the tester. Read the result, release the pressure, the r and r in number two... Till done.

Post it!