what would cause pulsing with nos.
Thread Starter
Drifting
Joined: Apr 2003
Posts: 1,379
Likes: 4
From: rome ny
what would cause pulsing with nos.
running a 100 shot nos superpowershot system on a holly carb fastburn 425 motor. the fuel and the timing are set fine but when i hit the nos im getting a higher end pulse. i was only getting 600 psi on the nos pressure gauge. seems like it could be a rich pulse. would i have this problem if i was giving to much fuel and not enough nos. fuel pressure is a 6.5 psi. the plugs seem to be burn ok, no detonation or ground strap discoloration. gap at .035 .
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
Re: what would cause pulsing with nos. (mos90)
Do you have a fuel pressure saftey switch?? When mine was set to close to actual fuel pressure it would pulse on and off. If yours is only pulsing at high rpm's I might be worried about your fuel supply. What are you running for a fuel setup??? The over richness from the low nitrous pressure won't cause pulsing.
Thread Starter
Drifting
Joined: Apr 2003
Posts: 1,379
Likes: 4
From: rome ny
Re: what would cause pulsing with nos. (mn_vette)
no fuel switch.i have a manual 130 gph holly pump run into a fuel pres reg set at 6.5. then one end of the pressure reg goes for the nos and the other goes to the carb. it seem to be starvin for nos not fuel. the plug show no signs of lean at all.
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
Re: what would cause pulsing with nos. (mos90)
I'm not farmiliar with the carb setups sorry, but I run my tank at 1000psi. The jets from the company come a little rich as it is, the pressure will only make that worse.
Le Mans Master
Joined: Oct 1999
Posts: 9,713
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From: Sachse Texas
Cruise-In I Veteran
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Re: what would cause pulsing with nos. (mos90)
You need at least 850 psi in that bottle before it will really even hit. 950-1050 is optimal and will give you the best results. I can run a 150 shot at 750-800 psi and I only get about a 50 shot out of it that is super rich. Over 1100 and you are on your own as far as the fuel curve is concerned (lean).
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Melting Slicks
Joined: Oct 2003
Posts: 2,951
Likes: 3
From: Mount Vernon OH
Re: what would cause pulsing with nos. (Phobos84)
Check your spark plug gap and if it is really wide you may want to tighten it up. If your plug gap is in the 35 range then put on an ignition box such as an MSD 6AL or higher. Bottle pressure can make a difference because your engine is experiencing a huge rich condition when you only have 600 psi and it will absolutely cause the engine to pulse especially as the rpm range climbs. Anyone who does not believe this should launch your car on with the nitrous system turned on but with the bottle valve closed...it will bog your engine big time. When you are fat your engine does not have the ability to burn the extra fuel that the nitrous system supplies and this can be part of your problem. I have found that with my current setup my ideal bottle pressure range from 950 to 1050 and anything higher I have to compensate with a slightly larger fuel jet on the system (not carb jet). Feel free to contact me by e-mail and I would be glad to help you. smille27@columbus.rr.com.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
Re: what would cause pulsing with nos. (crheinish)
Check fuel pressure it sounds high for a carb engine with nos. we use 3 1/2 to 4 psi on fuel system bottle has to be at a min of 950 as you travel down the 1/4 mile the bottle will loose pressure and if you started at 600 you had nothing to give the engine at the end of the run your compression would over ride bottle pressure. 
get a bottle heater or a good presure gauge. 
get a bottle heater or a good presure gauge.