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jalexquijano

Back And Forth Shaking Started While Accelerating In 1St Gear

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I had 4 days that i did not used my car since last sunday. Car was cold! pull the choke to start it and left it on for 5 minutes. I have the idle set up at 900 RPM with headlights on. Once i backed off the choke cable, the car presented the following problems:

 

1. Shaking back and forth when accelerating in 1st gear.

 

2. Backfire / Popping in 1st and 2nd gear.

 

Turn back home: the first 3 plugs from the front carb were okay. the last 3 ones were black. I am using NGK BP6ES spark plugs and Castrol 10w 30 engine oil as damper oil for both carbs. Am i missing something here? I did a vacuum test spraying carb cleaner to each an every hose near the carbs and at the brake booster and did not noticed any change in idle.  

 

The idle mixture knob / Screw is turned counterclockwise 3.5 turns which in my opinión is a lot. Should i keep turning until 4 to richen the mixture or is there something else i shall check?

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While I don't have SU carbs on my car, your post suggests several things.

 

First black plugs indicate rich running, so increasing the idle mixture would enrich an over rich mixture even more.

 

You idled the engine with the choke on for 5 minutes. SU carbs actually don't have a choke per se, they have an enrichment function. Again idling with enrichment for an excessive period would tend to lead to carbon fouling. It is not unusual to see some carbon fouling while running rich that burns itself off after a few minutes of normal operating conditions.

 

The fact that you found a difference between the front and back cylinders indicates different operating conditions between the carbs. Either that or you fouled the back plugs so bad that they were miss firing once enrichment was turned off and you were essentially running on three cylinder. Check enrichment functions work identically on both carbs.

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THese carbs are recently remanufactured by Ztherapy, meaning they are Brand new! Shouldnt both idle mixture knobs be turned equally? 3.5 turns each??

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2.5 turns, like the DVD shows.  Turn them towards the passenger's side, all the way up, then turn them out towards the drivers side 2.5 turns.  I live near the Gulf of Mexico and have mine at 2 turns out.  I've never been to Panama but it seems like I've read that's a tropical climate and choke isn't needed.  My car stays in 60 degree garage and my chokes are only pulled for 1 minute at the most.  Sounds to me like you are using the choke as an idle adjusting mechanism.  Are you using an air synchrometer to balance them individually with the screws by the dome tops?  That's the way to set the idle.  Your rear carb is out of adjustment or the float level is too high which could occur during shipping, it's covered in the DVD.

 

Maybe watch the DVD again, it's extremely helpful.

 

 

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Got an old school mechanic who came to my house today and inspect the car. After lifting the valve cover, He found out that the engine valves were too tight and will need to adjust them all. He did not brought his feeler gauge and will need to take care of that on monday. He is quoting me US$100 for the following:

 

1. Valve adjustments which according to my Schneider 274F cam should be set to  0.8 and 0.10. Am i correct?

 

2. Timing Chain and distributor adjustment.

 

He also noted the car is leaving black residues out of the muffler due to the bad valve adjustment. Is there any additional recommendation i can give him before he starts to adjust the valves? The shop that installed the cam has followed all the steps mentioned in the Hayes Manual and adjusted the timing to 10 degrees. Maybe here is my problem and after all this adjustements are concluded, there will be no more hesitation in 1st gear and backfiring,enabling me to adjust the carbs to 2.5 turns.

 

Any opinions?

Edited by jalexquijano

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If you drove it much with the valve lash too tight you might have damaged some valves.  "Burned", or warped.  Without feeler gauges though, it's hard to see how your "old-school" guy could tell that the lash was too tight.  I don't know if I'd use that guy.  Why not take it back to the shop that installed the cam?

 

You didn't address John Coffey's post at all.  Could the choke be stuck?  Seems like a carburetor problem.  Three black plugs is too rich, not bad valve lash.  I wouldn't let the old-school touch the car.

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To add to previous post, after pulling the choke, starting it, and pushing the choke lever back, if you can push one of the nozzles up with a finger, then it's sticking. Try Lithium spray grease on nozzle and choke linkage. Good to do that anyway.

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No problem, you're welcome.  Sometimes things are so obvious that they get overlooked.

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Valve adjustment has almost nothing to do with fuel/air mixture.  That is not the cause of your plugs fouling.  Your mechanic may be right about the valves being too tight but he's wrong about why the plug fouling and mixture.

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Okay with the valve rechecked and adjusted and the timing done, the car runs better. No backfire, just slight back and forth hesitation when running the car at the moment of releasing the clutch and engaging 1st gear. To avoid this either you step softly in the gas pedal or Hard. My uncle who has dealt with carbs before says it could be the float level in the carbs. Problem number to is the idle. If i leave the car parked in idle for more than 10 minutes rpm starts to drop from 1050 to 700 and goes up again. The engine does not shut down.

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John,

 

Same problem! Here is picture of the spark plugs and the distributor! I have no backfire in the front intake. I have the front carb set at 3.5 turns and the rear 3.25 turns. Still hesitation when releasing clutch and engaging first gear. Either i step smoothly on the pedal or step hard, otherwise hesitation begins.

 

Another problem i still have is the idle. If i leave the car in the parkway at idle for more than 10 minutes, it drops to 700 and rises back to 1000.

 

What a hassle!!! Hope someone here can point me out in the right direction.

 

 

 

Valve adjustment has almost nothing to do with fuel/air mixture.  That is not the cause of your plugs fouling.  Your mechanic may be right about the valves being too tight but he's wrong about why the plug fouling and mixture.

 

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If you drove it much with the valve lash too tight you might have damaged some valves.  "Burned", or warped.  Without feeler gauges though, it's hard to see how your "old-school" guy could tell that the lash was too tight.  I don't know if I'd use that guy.  Why not take it back to the shop that installed the cam?

 

You didn't address John Coffey's post at all.  Could the choke be stuck?  Seems like a carburetor problem.  Three black plugs is too rich, not bad valve lash.  I wouldn't let the old-school touch the car.

 

Well Zed Head,

 

I guess you were right. My mechanic has the same opinión as yours, he found the valve too tights and even though he manage to set them at 0.9 and .10, the car is still presenting the back and forth hesitation under 3000 rpm. If you pull the spark plug boot on cylinder 3 the idle does not drop down in comparison to the other cylinders. He believe some valves could be burned. He recommended to purchase the following:

 

12 valves

 

valve guides

 

valve seats

 

and a gasket that goes underneath.

 

I have both of  the idle mixture knobs set to 3.5 turns.I took a picture of the 6 spark plugs (BP6ES) Factory gap at .028 once i came back home starting from cylinder 6, left to right.

 

Please give me your input, if i should settle his opinión and where should i purchase good quality valves, valve guides, and valve seats.

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Edited by jalexquijano

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I wouldn't worry about the valves, valve guides, etc.  Your plugs indicate the engine is running lean.  Now that the valves are adjusted check your timing and make sure it matches the factory spec.  If you don't know what that is, set it to 10 degrees BTDC and 850 pm.

 

Check the float level on the carbs, set the idle mixture, and balance (sync) the carbs using a Synchrometer.

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Just did a compression test on the cylinders and a fuel pressure test.

 

THe compression test drew the following results:

 

Cylinder 1 : 180 PSI

 

Cylinder 2: 180 PSI

 

Cylinder 3: 185 PSI

 

Cylinder 4; 180 PSI

 

Cylinder 5: 180 PSI

 

Cylinder 6: 175 PSI

 

The fuel pressure was 3 PSI. I am running A Carter P60504 Electric Fuel Pump. Is this pressure enough for both carbs?

 

http://www.summitracing.com/int/parts/crt-p60504/overview/

 

I have both carbs set to 3.5 turns and i am still having a back and forth motion after stepping on the gas and releasing the pedal before reaching 3000 RPM.

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Fuel pressure on the low side per FSM but ballpark. Should be OK for ordinary driving. If you have a fuel return line you can block it off; that will raise fuel pressure a little. You could see if it makes any difference, I doubt it though.

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As John mentioned earlier, you really need a syncmeter to balance the carbs. I relied on my MK III calibrated eyeballs to ensure my Weber idle speeds were set identically. When I finally got a syncmeter, I was surprised to find one carb needed an additional one full turn to balance.

 

We tend to assume zero manufacturing tolerances when we don't have the tools - this almost always ends up biting you in the butt.

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As John mentioned earlier, you really need a syncmeter to balance the carbs. I relied on my MK III calibrated eyeballs to ensure my Weber idle speeds were set identically. When I finally got a syncmeter, I was surprised to find one carb needed an additional one full turn to balance.

 

We tend to assume zero manufacturing tolerances when we don't have the tools - this almost always ends up biting you in the butt.

I want to get rid of the back and forth hesitation under 3000 RPM.  It even happens after i pass a Street bump, where i need to slow down and shift to first again.

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I think we need a better explanation of what you mean by "back and forth hesitation".

 

Are you talking about the engine rocking with each revolution or are you talking about the rpm surging and retreating under a steady throttle?

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He could have the "sticky pedal" issue my red 240 has.  I haven't fixed it yet so I can't offer any advice other than what I've read about a cable being used instead of the rod.

 

EDIT: "Sticky Throttle Linkage"

Edited by siteunseen

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