4500 rpm, What is the Problem?

[Curtis]

I have someone trying to help me figure out what is going with the car. But if someone here can give me some advice I would appreciate it.

This is the car I am finishing up the restoration on. Let’s see if I can remember the timeline on it. I bought the car in 2002 or 2003. It had the original 1600 engine in it. I drove it for several years as is and the engine was a bit tired but always started and always ran fine.

I was then was offered an H20 stroked 1600 engine. I had the head refreshed and put it in and had some trouble it seemed with overheating. Pulled the engine and had the deck cleaned up. I also put in a street grind cam I had. That led to the learning debacle of the tale of two cam gears, SAE and metric and not mixing cams and gears.

I hated the crappy interior and this became the full restoration when the rude surprise of rust was found. And now we come to the present. Engine was torn down and the leaky rear main seal replaced. Correct cam gear and cam pairing.

Put on the fresh Z therapy carbs only to have trouble with them because of a sticky choke. Also put in the 123 distributor. It was not curved correctly so ran bad in the lower RPM. Back to the points distributor which was then rebuilt from 3 others. Put the original SU carbs back on also. Now runs fine in the lower rpm. Car pulls really well up to 4000 rpm then at 4500 craps out and pops.

Just discovered points distributor was giving too much total advance. Recurved the 123 and it is good. Put in flamethrower coil, new plug wires, gapped plugs, and today tried the Z Therapy carbs again and electric fuel pump. No change. As soon as you shift down the power returns. I’m on the verge of putting everything up for sale and buying the Jaguar F type convertible I want.

Well, what do I do to solve this?

[Curtis]

Also checked the new valve springs for any failure and adjusted clearance.

[notoptoy]

Curtis, what have you done about the whole fuel delivery side of the equation? Are you running the stock fuel pump or electric, are fuel lines clean with no air leaks or cracked rubber, tank pick up clean, etc. etc.?

[theunz]

Could be fuel delivery problem Curtis. A member on the Porsche forum was having a similar problem and the following test was recommended by Paul Abbott, a recognized Weber carb expert. While I realize that you are using SU’s and a mechanical pump instead of 3 choke Weber’s and an electric pump, this check could easily be adapted to your situation. Worth a shot?

I recommend checking fuel flow using the following setup to replicate real time fuel delivery:
disconnect fuel line to one of the banjo fittings at the carbs
using 5/15" "tee" fitting install a fuel pressure gauge into the line
on the third connection of the "tee" run a line into a fuel catch tank
place a pair of vise grip pliers (needle nose if you have them) onto the line to the catch tank
turn on ignition and adjust vise grip pliers until 3.5 psi is indicated on the fuel pressure gauge
fuel flow in gallons/hour (0.036 oz/second) should be equal to 1/10th of rated engine HP (a 160 HP engine would need 16 GPH fuel flow)

Side note…I find it interesting how long it takes some posts to show up. When I wrote my reply notoptoy had not responded yet. Even though it only took me a few minutes to respond, there is about a 30 minute gap between our post times. Sometimes responses to my posts happen almost instantaneously. My crappy internet, the poster’s internet, or server issue?

[Curtis]

I'll have to hunt down a pressure gauge and tee. Had to read that a couple times before the light went on. I was suggested to do a flow test yesterday. The stock pressure is stated in the tech specs to be 4.26 psi.

I hooked up the electric fuel pump last night and there was no change. Ironically this is the fuel pump that got the car home when I bought it and the stock pump failed going up I-5 by Mt. Shasta. We had just been in Redding for a gas stop and met a couple guys hauling home a Morris Minor frame. I had trouble getting it started and then off it went only to fail on the hill and along they came and helped us. The one guy was driving me back to Redding and at the top of the hill at the exit to turn around and go back was the lake and marina. Went to the boat shop and bought a pump.

You can see the fuel running through the filter at a good volume. The original set up ran fine and now it doesn't, beyond me. If only it was wires.

[Gregs672000]

Now would be the time for a wideband, but since that's not available (?) then it's time to go old school and read plugs. You know the routine if you've dug into my many posts... take her out to quiet spot where you can hold the rpms for as long as you can while it's missing, install the new plugs "in the field" (optional, but may give a clean read vs having driven to the spot with the new plugs), run her for some time, then shut the throttle while turning off the ignition and coast to your safe spot. Pull plugs (hot! Bring gloves) and see what they Say!

My experience with R motors is limited, but what you're describing is exactly what both of the Rs did when the timing chains were off a tooth... I truly hate to say that and hope I'm wrong. I'm sure it would be possible to determine where the cam is in relation to the crank with a dial indicator on the rocker, but I'm not set up or knowledgeable enough to do it. I also know you were very careful in regards to the chains and gears, so let's eliminate any other possibilities before we go there.

Curtis, I'm happy to take a look and add another set of eyes... 253 230-3484.

From your post above, "pops" usually means lean... if it's fuel.

[SLOroadster]

This sounds much like what I ran into with the 44 car at Monterey 2018. The engine might produce a harmonic that causes the fuel not to flow above a certain rpm. I cannot tell you how much hair I have pulled out trying to solve the issue on the 44 car. I checked everything from the exhaust to the ignition system to the fuel system multiple times. I had everyone who knows anything about roadster SUs trying to help at Monterey and no one got it right. Not even the Z therapy guy. I even tried different carbs and couldn't get the issue to go away. The solution turned out to be running the soft early carb mounts. THey look like 1500 ones, but are for the 1600, and are now impossibly rare to find. (It took me two years to find a pair of them.) I installed them on the car, and finally, the car would turn 7000 rpm.

Another solution might be to try a set of 2L carbs as they have rubber isolators between the carb body and the float bowls. The other less cheap solution is to toss the SUs in a box and install a set of 40 Mikunis and call it good.

Will

[Curtis]

I did a flow test and it is getting plenty of fuel. I may have an answer in a while.

[Curtis]

Okay, I seem to have an answer. On suggestion from one of the members I did the choke pull trick which I had forgot about. I had turned the carbs out to 4 turns already and the problem was slightly better and once it broke through to just above 5000 it ran again. Before I couldn't get it to 5k. Then did the choke and it completely disappeared. Stopped and turn it to 4 and a 1/2 turns and it was better and required the slightest choke.

I have the ADQ(?) needles in it right now. I'm going to switch back to stock needles and see how it does. Unfortunately I have a bad vibration going on and need to solve that before something very bad happens.

[Curtis]

Wrote to Keith and he thinks I need richer needles. He is sending me some.

[Curtis]

Problem almost completely gone. Had to turn the carbs to 5 turns. Only the slightest hesitation now. Might go to 5.5 until I get the new needles. But it does me little good until I find the source of the vibration.

[23yrRebuild]

I know different engine configurations might allow for a wide variation of "turns out" on SU carbs, but 5 to 5.5 turns really does seem like a lot to me. I'm running exactly 1 1/4 turns out from fully up, on my R16 stroker with 9.5 compression and Booinie EI. My ADQ needles are also set out 0.015" from flush on both of the SU pistons. Your 5 turns out to run rich enough to smooth things out, makes me wonder about your float level / needle and seat adjustments.
Just a thought....
Mike

[DAC21]

Problem almost completely gone. Had to turn the carbs to 5 turns. Only the slightest hesitation now. Might go to 5.5 until I get the new needles. But it does me little good until I find the source of the vibration.

Is the vibration when the car is stationary (idle) on the road, or both?

[Curtis]

Under power. You put in the clutch and it goes away. I checked the driveshaft yesterday to make sure the alignment arrows were good for the two pieces. The exhaust has been all redone to make sure there is no frame contact.

Motor mounts are good and transmission mount was checked for any contact. The new header was nearly or was touching the block at oil pan so it got a relief put in to the pipe.

[DAC21]

Under power. You put in the clutch and it goes away. I checked the driveshaft yesterday to make sure the alignment arrows were good for the two pieces. The exhaust has been all redone to make sure there is no frame contact.

Motor mounts are good and transmission mount was checked for any contact. The new header was nearly or was touching the block at oil pan so it got a relief put in to the pipe.

Maybe ask Keith?