Carb problems help Don, anyone

[mkcobra]

I have a mildly modified 351W with eldelbrock heads, 750 carb, and MSD dist should be making right at 400hp per Dyno sheet. Don i think this is your standard 351W setup. i ran it on the Chassi dyno and found a problem, it doesnt make HP. infact it seems to jump to 215 hp at 3200 rpms and then only climbs to 244 by 5800 rmp almost flat. it does seems to pull strong on the road but not like a 400 hp motor would. it also seem to struggle when the rpms go up. any ideas, fule mixture is very weird also starts at 13 then drops at 4000 to below 10 then back up to 12 at the very end. almost looks like a large V shape not like any other curves we have seen. i am questioning the carb like maybe the secondaries are not opening. I am a little new to elelbrock can you adjust the secondaries to open and when. its a model 1407, heads are the 6025 aluminum. any help would be appreciated.

thanks

[dscott]

mkcobra, The Edelbrock carb is pretty foolproof but there could be a problem. I think I would pull the top off and check for dirt or debris in the bowl. Also, on the top of the carb on each side of the choke plate there is a small cover with a screw. These are the metering rods to the main jets. You can remove the covers and the rod with the spring to see if there is any damage or binding of the rods. Check the fuel filter, and the pump. You could also check for any vacumn leaks which would cause a problem like this. Timing should be checked for full adavnce at 3500 rpm. between 32 and 34 degrees will work well.

The Edelbrock has mechanical secondaries with a vacumn plate on top of the butterflies. If you open the throttle you should be able to open the plate and look at the secondaries to make sure they are working. There is no adjustment. The vacumn plate should operate freely, make sure it's not binding.

Fuel mixture should stay around 12.5 for this type of engine. You're not too far off. Optimum for a stock engine is generally at 14 to 1.

One thing to remember on the Classic is the hp loss through the sidepipes. It's easy to lose 40 or 50 horsepower there. The drive train should have a loss of around 15%. Even with those losses you should still be around the 300hp mark at the wheels. You can have your mechanic call me if needed.
Don

[mkcobra]

I have the timing set at 36 degree, and all the carb parts seem freely moveable and working. i am at a loss. cant post the graphs due to file size, I will try the draw it or upload the text version. this week end we are back on the dyno and will try and tune and evaluate further.

thanks Mike

[mkcobra]

Cool hope everyone can see the dyno sheet .

[mkcobra]

maybe a little easier to see the graph.

[mkcobra]

come on guys , dont tell me i stumped everyone. if you need more info ask questions or email, I may even be temped to offer a HP reward the first one to have the right answer and find me 70HP could get 50.00 cool ones. lets see what comes up.

thanks Mike
wishing he had more ponies.

[flipper35]

The secondaries can be adjusted according to the manual by adding or removing weight to change when they open. I agree also to check the metering rods.

[mkcobra]

We did change the metering rods to one step up per the book but not really changing the airfuel reading, i do have one more larger rod. on the secondary you are saying to cut weight off of the butter fly it looks like one solid part with the weights on the ends, i will watch the carb running this weekend to see if they open and how much. thanks

[Cobra Chuck]

Originally posted by mkcobra
come on guys , dont tell me i stumped everyone. if you need more info ask questions or email, I may even be temped to offer a HP reward the first one to have the right answer and find me 70HP could get 50.00 cool ones. lets see what comes up.

thanks Mike
wishing he had more ponies.

You told us about all the neat bolt on performance stuff but never said a thing about the bump stick. Without an well matched performance cam you will never get the ponies. The cam is really the performance brain of the engine. If you are only slightly lifting the valves for a very short period of time in each cycle, the badest ignition, manifold and carb are not going to buy the ponies. Get out your cam card and tell us about the bump stick.

Cobra Chuck

[Cobra Chuck]

Originally posted by mkcobra
We did change the metering rods to one step up per the book but not really changing the airfuel reading, i do have one more larger rod. on the secondary you are saying to cut weight off of the butter fly it looks like one solid part with the weights on the ends, i will watch the carb running this weekend to see if they open and how much. thanks

Another non carb suggestion or question. Tell us about the MSD distributor please. Is it a mechanical or vacuum advance? If it is mechanical what set of springs are in the advance mechanism. My MSD distributor came with three spring sets for different timing curves. I know the distributor has nothing to do with the low fuel air ratio but you are looking for HP right? and HP in all the right places, ignition timing can really screw things up.

I am using the 6025 heads, 1407 carb on a 302. I haven't had it on the Dyno yet and I have been running with shop wheels and tires but I know one thing it kicks some serious butt. I also know without a air fuel analyzer that at idle it runs rich and doesn't lean out much through the rpms range. I am running a Ford Racing M-6250-B303 roller tappet cam.

Cobra Chuck

[Bill E]

What do the plugs look like? Did you do a compression test. get a new exsost system. go over the firing order, some cams have a different one three are 3 Make suer which one you have don't assume change the chip in the MSD

[mkcobra]

well, the cam is a comp extrem energy 262 490 intake 500 exhaust 290 duration mild . the distr stock MSD billet, stock springs 2 heavy silver, total advance is 36 at 3600 rpm. idle is set at 12, mechanical only model 8584.

cobra chuck , mine to seems to hit hard on the street, the TKO 5 speed with 3:55 gears make nice tire smoke launch seems easy but as it revs up it looses power. you should jump on a dyno . the great torque at the low end helps feel, but this motor should be at 350-320 at rear wheels . any more questions. thanks this is helping me think through things also . i was at first worried the cam was to small. but Edelbrocks performer 351 package is almost identical to mine and they had 400 HP as well.

[mkcobra]

Bill E the plugs show some mild black soft soot on a few the other tan to dark tan , i havent pulled all 3.
I am not sure what you mean about the MSD dont know how to change the chip and how would this help. havent done a compression test will get one hopefully tomorrow. when i retorque the rockers.

[Jack21]

Bumpstick is a little mild, but shoud be OK for mostly street driving. Peak HP should be 5000 - 5500 RPM.

Distributor advance is coming in a little slow. Total of 34 - 38 all in by 2500 - 2600 RPM. Higher compression=less lead.

My gut, looking at your dyno curve, tells me you're using stock CR sidepipes, which are choking your engine. The little 1 1/4" pipe inside the muffler would make the HP peak fairly low, and stay flat across the powerband because the exhaust can't flow through the muffler any faster. Cut the mufflers out and install 2 1/2" or 3" core glasspacks, and the power curve should look more like what you expected.

Page Muffler in Arizona makes a 2 1/2" ID, 4" OD, 30" length that flows reasonably well, and is not overly loud. J.C. Whitney has a 3"ID, 4" OD, 30" length that flows a little better, but is a little louder. My "winter" muffler, also from Page, is 2 1/4" ID, and 36" long. They do cut the power some but are very mellow for street driving with the top and sidecurtains on.

[mkcobra]

Jack21

this sound more consistant with the weak flow, and quick powerband, little in or little out. Don say the pipes only cost about 50hp if you take that off of the 419 or 400hp motor still should be 350, with drive trainloss still should make like 300hp at the rear wheels. I may consider disconnecting the pipes at the header just to see the increase. Jack is see you to have a CR 351 , did you get to Dyno yours and what kind of HP are you making.

Don can you comment on some simple bolt on replacements for what i have, these seem loud already not sure of the exact info on this pipe but sound good an look nice, how can i tell what size mufflers are in this sidepipes.

[Cobra Chuck]

Originally posted by mkcobra
well, the cam is a comp extrem energy 262 490 intake 500 exhaust 290 duration mild . the distr stock MSD billet, stock springs 2 heavy silver, total advance is 36 at 3600 rpm. idle is set at 12, mechanical only model 8584.

cobra chuck , mine to seems to hit hard on the street, the TKO 5 speed with 3:55 gears make nice tire smoke launch seems easy but as it revs up it looses power. you should jump on a dyno . the great torque at the low end helps feel, but this motor should be at 350-320 at rear wheels . any more questions. thanks this is helping me think through things also . i was at first worried the cam was to small. but Edelbrocks performer 351 package is almost identical to mine and they had 400 HP as well.

mkcobra it sounds like the bump stick is ok. Of course if you flatten out the stick in the first few hours of operation that could still be the problem. If cams are going to go they usually do it early on usually in a few hours. If they are not hardened right or you did not lube it well during assembly you can flatten out a cam quick. Also you mentioned retorquing the rockers, are you sure you had them lashed right to begin with? If you are still getting the specified lift and duration on your cam (pain in the ass to check) and you have lashed or preloaded your rockers right then about the only thing left is compression check, carb. adjustments and most likely a low flow exhaust system. I would call CR and find out what the measurements are for your system and ask them about this problem. It sounds like you were already expecting a 50HP hit on the exhaust. How many hours on the engine?

Cobra Chuck

[mkcobra]

Sorry guys down here in TX rain rain rain. i didnt get to work on it at all yet , i will hope later in the week we will get it back on the dyno. so far to things seem close one the dist curve is stock and we can change springs and bushing . second the exhuast maybe the limiting factor if it really only has 2 small tube . 400hp needs at least 2 1/2 inch pipes duals for near optimum performace based on multiple exhaust companies.

Cobra chuck lets dont go there on the flattend cam, it only has 1400 miles on it hate to think my cam is toast but would love to bump it over .520 if i need a new one.

[Cobra Chuck]

Originally posted by mkcobra
Sorry guys down here in TX rain rain rain. i didnt get to work on it at all yet , i will hope later in the week we will get it back on the dyno. so far to things seem close one the dist curve is stock and we can change springs and bushing . second the exhuast maybe the limiting factor if it really only has 2 small tube . 400hp needs at least 2 1/2 inch pipes duals for near optimum performace based on multiple exhaust companies.

Cobra chuck lets dont go there on the flattend cam, it only has 1400 miles on it hate to think my cam is toast but would love to bump it over .520 if i need a new one.

Good news about the distributor. It sounds like your research is paying off with the exhaust news. I am not familiar with CR exhaust size but it sounds like for whatever reason they have the exhaust pinched down pretty small. My LS427 headers and side pipes are 1 3/4" pipe each cylinder to the collector, from collector to muffler is 3 or 3 1/4" into a muffler that is 4" or better and back to 3 or 3 1/4" exhaust tail pipe that is 4" long. The DS / PS headers and side pipes are not tied to together. It will be interesting to see how much back pressure I am generating with this set up. Please describe your exhaust system a little bit better.

Cobra Chuck

[coyled]

Mkcobra, the fact that it gets so rich thru the curve after being close to perfect means that the exhast is so restrictive that it requires a leaner mixture. Take those side pipes off and dyno it again. Or, I wonder if your balancer has slipped giving you an inaccurate timing reading. I would check that timing all the way to 5500 rpm to make sure it is not retarding for some reason. If its in the mid 30's, I would bump the timing up 5 degrees and see if it makes a difference. If it makes a lot more power, then your balancer has slipped. Any motor with less than optimum timing will require less fuel in the power band. Good luck, Scott.