Technical Dual Stromberg 97 tuning

Interesting dilemma. You say that the carbs are flowing well at speed. I assume you can see down into them and see the fuel flowing from the nozzles. ( hate to do that in case of backfire). I lean more towards the distributor as a potential culprit. You say it is rebuilt but have you put a dwell meter on it? That always tells me if the points are doing there job or not. If they are set too wide, the engine usually runs at low speed but falls apart as it is revved up. I have a divers helmet distributor on mine and it works well. I gap my plugs at .025" and have not experienced any problems with burning contacts or such in the 15 years it has been on the road. I am watching this post with interest as I really want to know what you eventually find the problem to be.

 

Both distributors dwelled
3 helmet coils and a round modern style, changed out ballast resistor, 3 condensers, 2 sets of plugs and wires.....

And I can see the nozzles although my hairline is a little shorter from too much ether a while back!

 

Ok I have got a slight result.
Tried advancing the timing a mark at a time and it gradually improved a little. Distributor is now at full advance on the adjustment plate and is idling much smoother and revving up a lot cleaner but not perfect.

Tried my crab distributor to confirm result and it too ran better at full advance on the plate.

Pulled distributors off and checked timing using the two ruler methods and was too far advanced. Adjusts back to middle of scale - perfect on both and confirms the distributor machine results of Middle of scale but does not correspond with on car timing.

Timing light packed it in so will get another and check what is happening on timing marks.

In the meantime I am going to pull front cover and check timing gear to see if the dots are out of phase.

 

check that yet? Also if your using ethanol blend fuel you may need more jet, try quickly pumping the throttle in short strokes ( like your foot is nervous as hell ) thus generating a nearly steady stream from you accelerator pumps.....if that helps drill out the jets one number at a time...I had to go about three numbers on three of my trucks with the motorcraft- autolite 2 barrels since we were blessed with 15% ethanol shit in our gasoline here in the land of high taxes and corruption!

 

New exhaust fitted with dual smithys mufflers.

 

WOW! Good luck, very frustrating getting these simple machines to work properly

 

Good to see you are getting some results. I think that pulling the timing cover and checking the timing marks is a good idea. For your info, my diving helmet distributor runs full static advance (which only allows for a couple of degrees more than suggested timing) and I removed the vaccum brake so the vaccum advance is full on at all times. Only the mechanical advance is operative. I run high compression heads and have not experienced any pinging. The flathead distributors do not allow as much timing advance as modern distributors. You can dial in more advance because the gas is better quality now than back when. And it doesn't require high octane gas.

 

Ok. I had the front cover off. Pressed on timing gear in great condition and both the alignment marks on cam and gear line up and both crank and cam marks align correctly.

Pulled intake and confirmed all valve movement is at correct timing with TDC mark.

Put on a stock manifold and one carb and fired it up. No change. Tried the other carb and no change. Rebuilt a third 97 from the stash and it ran marginally better but not by much.

Confirmed good strong spark at each plug and no missing sparks by earthing each in turn. Tried 3 timing lights and none would flash??? Tried on OT car and flash. Don't know what is going on there but will keep trying tomorrow.

Also built a degree wheel and marked TDC, 4 degrees BTDC and 20 ATDC for reference when I sort out the timing light issue.

Pulling a 97 from a known strong running single carb engine and will also test tomorrow.

 

Do you mean to use the timing light on each spark plug wire?......replace that coil...

 

What cam is in it? A well-known cam maker was reported in the last few years to have made some flathead cams with horrible quality. Like multiple degrees off. I won't name any names until you give your answer.

 

I check with a timing light on multiple cyls to watch the spark flashes and that there aren't any missing. Gary

 

Now that's a good idea....This is an great thread & it will be interesting to see what the problem/fix is. Thanks for keeping us un to date and 'in the loop'.

 

Update. Known good carb made no difference. Confirmed I have good strong and steady spark at each plug wire. Due to the lack of result from both fuel and spark tests I have decided to dig deeper.

Intake is back off and I have confirmed lifter action is occurring in correct sequence with cam timing. Next plan is to check the valve spring lengths from info I found in a old ford manual for both closed and open valves. If I see a difference in length from those measurements it may show weak springs. From the manual it says that the springs may allow the valves to close sufficiently for a compression test at idle but may be lazy under load. The test procedure worries me a little as it says to drive at 15mph with the brakes gradually applied to induce load and then check compression on each cylinder in turn. If there is a loss under load I may have found my problem. A long bow to draw I know but I am running out of options.

 

Did you hook up a vacuum gauge and get a good reading? That usually shows a valve problem amd a host of other things. Gary

 

I know you have probably ruled out carburation due to using known good carb, however, just want to pass on what I found this weekend on my car with dual 97s. Started good, revved good as long as you were working the throttle, but like you would die when letting off from full throttle. Would start right back up, idle good for 6-7 secs then start blubbering and die with fuel coming out the accelerator pump shaft hole. When I went to check float level I found the fuel inlet fitting on front carb to be damaged at the crimp holding the check ball (stromberg version of needle and seat). The crimp was broken about 3/4 of the way around. Installed new inlet valves on both carbs and runs near perfect now. Probably no help for you but someone else may be having this problem. Also, I believe this valve was faulty from the start, as I had never had it off since purchasing the carbs a year ago.

 

I had low vacuum (14-15) with the dual intake and have it fluctuating between 16 and 18 now. It sometimes evens out and holds steady and then starts fluctuating which has me thinking valve issues.

As to the cam, I have no idea but it was in the engine when I got it. No identifying marks on front of it that I can see. As it was pulled from a car that was getting a 350 conversion at least several years ago I think it may be stock or at the very least mild cam. Idle is a little choppy so hard to tell.

 

Made some measurements tonight. All lifter gaps are correct, cam lift is correct on all valves, spring lengths with valves closed are all correct. That eliminates cam or lifters as being suspect.

Next will be to reassemble it all and pull the exhaust and see what happens.

 

Success. After reassembling everything and no result I went inside and moped. My wife said "have you changed the plugs?" And I said of course I did. She reminded me that was two months ago when all this started.

Next day bought a new set of plugs and fire it up. Idle was incredible and a 70 percent improvement. This got me thinking so I pulled all the leads in turn and confirmed I had a good strong blue spark that jumped 1/2 inch at least. While discussing this with a buddy I suggested doing the same procedure but revving the engine up to the zone where it falls over. We tried it and saw the spark lose intensity and struggle to spark over 1/8 inch. This made me think condenser but as I had been through a heap of them I didn't want to waste more money. Then I remembered a thread on the HAMB I read recently about VW beetle condensers. Why not I thought.

Went to the only parts joint in town and they had one in there discount area as discontinued stock. Guess freaking what? Fucker fired up and ran stronger than it has ever been!

Now I will recheck the timing and once all looks good will go back to the Thickstun and duals and see what happens.

Thanks all for the ideas and help to work my way through this. I will update again once the duals go back on.

 

That is great news! Isn't there a saying "most carburetor problems are ignition related" ??

 

I know, right? Been kicking my own ass over this. Was sure I was being thorough and systematic with the fault finding but the old adage (that I am generally the one preaching!) is don't trust new parts and what did I do?

 

Methinks you owe the little woman a dinner!

 

I am glad you got it figured out. Success is sweet, Gary

 

Good news. Great investigation. Went through this two years ago. Ended up being the condenser too after everything seem to point to fuel. Your work and explanations provided a great learning tool for future generations. Always takes a good woman to keep us on the straight and narrow.

 

Lesson...... Wife knows best!

She (they) will always remind us of that.

 

Whew, that was a ton of work! Good job and thanks for taking the time to post.

 

Note to self; keep a hand full of condensers in the trunk while traveling. Along with points, fan belts, hose clamps etc...

 

Dual manifold and carbs back on. All sounds and feels good. Yes I will be keeping spare condenser (VW style) in with my spare points, rotor etc.

 

Don't you love it when people keep telling you how "simple" flatheads are?
Glad you (she) figured it out. Happy Motoring!

 

Congrats on your success !...my mother(77years old) always interjects when my father or nephew are discussing motor problems to change the spark plugs!.....DANG mom was right again!

 

Had the same issue years ago....went nuts trying to figure it out. As always its the simple things that need to be eliminated first. In this case it was the plugs, duds - even thought they were not fouled and were almost new. An old bloke once told me - "first thing you do is swap out the plugs". That, and the coil are easy swaps.

Also had a similar issue in my 21 stud - couldn't find a decent condenser worth a shit so gave up and fitted a crab I rebuilt with a Pertronix. So far, so good.

Guess that still holds true.

Glad you got it sorted, any pics of the car?