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won't rev - unless I back off the accelerator..

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rvmeisen Avatar
rvmeisen Ron M
Loganville, GA, USA   USA
All,

just got a 72 Spitfire MK IV, my first so I'm new to them. it's an Early 1500 with a stromberg, Pertronix ignition, been sitting for a while but cranks well, idles a little rough.

It runs up through the gears fine except if I push too far on the accelerator, it bogs. If I back off it takes up and runs up as far as the throttle will allow.. I checked the oil in the damper and it was down, filled it with 20 wt but no real difference.

pretty sure the ignition / timing / advance is good because if I back off throttle, it goes fairly well. not saying they are perfect, just not the thing holding it back this time.



what's the best place to start?

Thanks
Ron

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Falkon Avatar
Falkon Al Martin
Appleton, WI, USA   USA
Change the fuel filter first.

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rvmeisen Avatar
rvmeisen Ron M
Loganville, GA, USA   USA
Doesn't have one that I can see, not anywhere from the tank or between fuel pump and the Carb.. Is there a filter in the Tank itself?

I didn't think so..

(I'll add one when we get this sorted though..)

Thanks

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carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
90% of carb issues are electric. Never assume, always check. Start with the timing.



'S all for now
Vic

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Outfect Avatar
Outfect Dave B
La Sal, UT, USA   USA
1940 Ford N Series Tractors "Henry"
1951 Other Not Listed "SnowMan"
1979 Triumph Spitfire 1500 "White October"
1980 Triumph Spitfire 1500 "Tangerine Dream"
Ronald,

Fuel filters or the rubber diaphragm in the Stromberg has a tear/leak. It will work with a
tear up until a point (3000RPM or so) then the piston will not be sucked up any further and that's
as fast as the engine will turn. Check the archives here as there are probably many threads on how to change it.
2 tabs that must be placed in the proper position and the holes in the bottom should evenly face the motor. Not too expensive.
Maybe $3-$5 plus shipping. Might as well get the whole carb kit.

Could also be a fuel filter. You never know until you know. Welcome to the world of old British cars.

DaveInUtah


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  Herald948 thanked Outfect for this post
Wolfcreek Steve Steve P
Central, WI, USA   USA
1937 Dodge Magnum "The Dodge"
1947 Unknown Unknown "My Autocar"
1980 Triumph Spitfire 1500 "Vicki's Little Red Car"
Could also be the ignition condensor, as cylinder pressure increases, spark won't jump across the plugs. I've seen it hundreds of times on Briggs and Strattons

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Outfect Avatar
Outfect Dave B
La Sal, UT, USA   USA
1940 Ford N Series Tractors "Henry"
1951 Other Not Listed "SnowMan"
1979 Triumph Spitfire 1500 "White October"
1980 Triumph Spitfire 1500 "Tangerine Dream"
Steve,

In reply to # 1601103 by Wolfcreek Steve Could also be the ignition condensor, as cylinder pressure increases, spark won't jump across the plugs. I've seen it hundreds of times on Briggs and Strattons


He has a Pertronix.

DaveInUtah

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Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
When the ZS is low (or out) of oil it acts like a regular carb with a faulty accelerator pump.

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Manana Avatar
Manana Steve Wten
Thornhill, ON, Canada   CAN
I think I'm with Victor. It takes very little time and effort to retard the timing just a bit. If it improves you can look more closely at accuracy, if not just put it back as it was so you don't alter too many parameters. As always easy and cheap first.

Good luck with it.



Steve
http://stevew10.wix.com/spit16

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clshore Carter Shore
Beverly Hills, FL, USA   USA
In reply to # 1601140 by Manana I think I'm with Victor. It takes very little time and effort to retard the timing just a bit. If it improves you can look more closely at accuracy, if not just put it back as it was so you don't alter too many parameters. As always easy and cheap first.

Good luck with it.

It's worthwhile to actually use a timing light to see what it's doing …
Between centrifugal and vacuum timing mechanisms, it does not (and SHOULD not) stay at one value as RPM and throttle position changes.

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rvmeisen Avatar
rvmeisen Ron M
Loganville, GA, USA   USA
Thanks for all the suggestions.

Timing looks good as does the spark (checked every plug just to cover Dist cap, rotor and wires). Timing is 9-10 Degrees BTDC and it moves when engine revs, it does not bog down with no load, will rev 4-5K (dash tach) no problem.

Drove it for a while and it got some better when it was warmed up well. It will gain RPMs as long as you don't push right to the floor. It will rev 4500+ in 4th and hold speed..

some more clues: used 2+ gallons of gas to go ~35 miles, Tailpipe is black and after you run for a while it will not idle. Running under 1500 with the throttle is very rough.
restarts require full open throttle and takes a bit to catch even then. After it sits for a while it will restart and idle.
have not pulled the plugs, probably see the same thing as the Tailpipe when I do.

Thanks
Ron

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POW Peter Wirth
HEBRON, NH - New Hampshire, USA   USA
I too think a very good place to start is the carb diaphragm. - Pete

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rvmeisen Avatar
rvmeisen Ron M
Loganville, GA, USA   USA
Thanks for the information so far, Now what exactly does it mean when the vacuum line to the distributor is full of gas, along with the air filter housing?
luckily no gas in the oil..
the diaphragm was good, like it was new but the screws all looked like the carb had not been open in a while. Can you change the diaphragm without pulling the carb off the manifold ?

Since it is flooding, is there anything I need to specifically look for as I break it apart?

got a full kit and ordered some extra parts that were suggested on other threads on here.but not the floats.

Again, thanks for the advise.

Ron

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Falkon Avatar
Falkon Al Martin
Appleton, WI, USA   USA
You're flooding. That's why it uses so much gas. Check the float level. I have a '72 also now. It's pretty easy to pull the carb off, and remove the bottom. Then make sure the float level is set correctly. Since you bought a rebuild kit replace the needle valve. These can leak also, and allow excess gas into carb.


http://www.marineengine.com/parts/technical_information/sierra_18-7085.pdf






Edited 3 time(s). Last edit at 2019-03-14 05:46 PM by Falkon.

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rvmeisen Avatar
rvmeisen Ron M
Loganville, GA, USA   USA
Al,

you were right on, the float was high and the needle/seat was sticking. It runs much better now that it's clean and float adjusted.

I need to adjust the idle (move the needle up, it's lean, quits if I lift the piston).
Next issue is I'm having an issue starting when it is hot.

If I shut it off and try to restart in under 1/2 hour. It spins for a minute and will start if I open the throttle. It runs rough until i clear it by reving it up. It doesn't blow black smoke like it did when it was rich.

What adjustment(s) impact that?

Thanks for all your help
Ron

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