SASPEEDRACER24 Posted June 7, 2010 Report Share Posted June 7, 2010 Have a Holley 4412 #80 Jets... Plugs and tops of pistons (at last rebuild) look like it is running rich. Does running pump gas (Super) make any difference for jetting vs. racing fuel...Thinking the carb had race gas ran though it on a regular basis before I got it... Also if I lean out the carb. I assume it will run hotter as you lean it out, so do you take some timing out of the motor to keep it from overheating or does it really make a difference. Thanks in advance for any input... Marc Link to comment Share on other sites More sharing options...
rpfan Posted June 7, 2010 Report Share Posted June 7, 2010 Have a Holley 4412 #80 Jets... Plugs and tops of pistons (at last rebuild) look like it is running rich. Does running pump gas (Super) make any difference for jetting vs. racing fuel...Thinking the carb had race gas ran though it on a regular basis before I got it... Also if I lean out the carb. I assume it will run hotter as you lean it out, so do you take some timing out of the motor to keep it from overheating or does it really make a difference. Thanks in advance for any input... Marc Never in 20 years ran that fat. Put 76 jets in it and leave the timing alone. JMO Link to comment Share on other sites More sharing options...
Truck99 Posted June 7, 2010 Report Share Posted June 7, 2010 Have a Holley 4412 #80 Jets... Plugs and tops of pistons (at last rebuild) look like it is running rich. Does running pump gas (Super) make any difference for jetting vs. racing fuel...Thinking the carb had race gas ran though it on a regular basis before I got it... Also if I lean out the carb. I assume it will run hotter as you lean it out, so do you take some timing out of the motor to keep it from overheating or does it really make a difference. Thanks in advance for any input... Marc Never in 20 years ran that fat. Put 76 jets in it and leave the timing alone. JMO Agreed Link to comment Share on other sites More sharing options...
sm44 Posted June 7, 2010 Report Share Posted June 7, 2010 i would much rather run fat than lean..... Link to comment Share on other sites More sharing options...
jwmbishop Posted June 7, 2010 Report Share Posted June 7, 2010 Running fat washes the oil off of the intake valve stems, rings and cylinder wall. When you pop onto the throttle that momentary lean as the accel pump hits will cause a very centralized hot spot - right at the comp ring gap where the seal (made by the oils tension) is most succeptable to wash off. then if the timing is too tall you will stress crack the piston. I've seen many distorted (melted) lands - even with a nice black coating to the top of the piston! Timing to total centrifugal advance at 32 degrees (34 on cool evenings) at 3200 rpm with 74-78 jets is a good safe starting point for sm block chev, big ports, 15" vacc idle cam and holley 4412. And yes a jump up one or two jet sizes (and 2-4 degrees less timing) for pump gas is not unusual. The ping resitance of good racing fuel allows leaner mix and more timing. The edge is finer and easier to cross with pump gas! Get a good lamp type microscope (radio shack has one for 20 bucks) and look at WOT results on your spark plugs. The first signs of trouble are bright shiny spots (stainless steel) on the radius of the center electrode insulator crown. the spots are from the flame ring of your head gasket molecularizing. a little leaner and dull grey spots start appearing - the aluminum from your pistons. the amazing thing is you would expect the piston to show first - but its cooled by movement and oil while the flame ring being stationary is hit by squish and cyl pressure. Too lean = blown head gasket. Too much timing = distorted ring lands or cracked spark plugs. Too lean with too much timing = melted piston (at best!). Link to comment Share on other sites More sharing options...
HiTech Posted June 8, 2010 Report Share Posted June 8, 2010 when i sit up our carbs ...i start with a safe jettting ..put in some new plugs . .get the car on the track and up to speed as fast as posible..[ dont want it to idle much ..] .run the car ten or so laps hard .....,and kill the motor at full rpm ..then check the plugs ..and go from there ..low rpm and high rpm is a very big differents in what you will find on your plugs ...decide on what color you want your plugs to look like so forth .. before i started doing it that way ..i lost alot of pistons ....havent lost one sense the mid 80.s ... everyone has thier own way .. this has worked for me ..i could have one motor running 72 jets .another maybe running .69 ..but no more that 76 ..... Link to comment Share on other sites More sharing options...
1-Crew Posted June 8, 2010 Report Share Posted June 8, 2010 Jetting used to be a black magic item but it does not have to be.. Plug color is an indicator but it only shows the last region of operation and that might not be the MAIN region of operation. There are wide band O2 sensor setups available for not much money. Cheap when compared to motor damage or even dyno time. Leaded gas will kill an O2 sensor but not immediately, you can get some very good info on carb operation before the sensor dies. For ~$300 you can get a good wideband sensor and meter to check real mixture while on the track. That tells you more than just jetting, it can help with power valve selection, jetting and accel pump selection. Link to comment Share on other sites More sharing options...
modcoupe71 Posted June 8, 2010 Report Share Posted June 8, 2010 Have a Holley 4412 #80 Jets... Plugs and tops of pistons (at last rebuild) look like it is running rich. Does running pump gas (Super) make any difference for jetting vs. racing fuel...Thinking the carb had race gas ran though it on a regular basis before I got it... Also if I lean out the carb. I assume it will run hotter as you lean it out, so do you take some timing out of the motor to keep it from overheating or does it really make a difference. Thanks in advance for any input... Marc Marc only Donald Lewis ran that fat with his 403 Olds engine after the quadro jet carb wasn't allowed any more. whats in the engine Marc? Link to comment Share on other sites More sharing options...
jwmbishop Posted June 8, 2010 Report Share Posted June 8, 2010 Jetting used to be a black magic item but it does not have to be.. Plug color is an indicator but it only shows the last region of operation and that might not be the MAIN region of operation. There are wide band O2 sensor setups available for not much money. Cheap when compared to motor damage or even dyno time. Leaded gas will kill an O2 sensor but not immediately, you can get some very good info on carb operation before the sensor dies. For ~$300 you can get a good wideband sensor and meter to check real mixture while on the track. That tells you more than just jetting, it can help with power valve selection, jetting and accel pump selection. Absolutely - the unit I have ran 379 and it records, displays real time and interfaces with a computer. Uses the VW wideband. Just make sure to install the O2 bung on the top half of the collector - ive seen folks place it on the bottom for ease - and very quickly loose the most expensive part of the setup - the sensor. When you shut down a hot engine the moist atmosheric air reversions in and forms condensation. This goes to the lowest point - if the O2 sensor is at a low point that moisture is then blown across the face at start up. Link to comment Share on other sites More sharing options...
Danielsen Motorsports Posted June 11, 2010 Report Share Posted June 11, 2010 Its possible the previous owner of the carb had a blown power valve and was increasing the jet size thinking that it needed more fuel. I would diffently check the power valve and drop the jet like others have stated. Link to comment Share on other sites More sharing options...
SASPEEDRACER24 Posted June 11, 2010 Author Report Share Posted June 11, 2010 Thanks guys... Gonna put 76's in change the plugs and see how it runs (temp. wise) before backing off on the timing any... Thanks for all the help... Link to comment Share on other sites More sharing options...
railer Posted June 12, 2010 Report Share Posted June 12, 2010 ok what about when you have a block off power valve you have to faten up the jets Is that correct??? then if you have the color of a paper bag color ,,is that good?? so what ya'll are sayin also if you run it too rich you could blow out the compression rings on all the pistons?? .... someone tell me why all the compression rings on all the pistons are broken ... the gap was right ,, piston to wall was right was it the fuel mixture??? shi//// I dont know running too hot of a plug??? what Link to comment Share on other sites More sharing options...
Crazyhorse Posted June 12, 2010 Report Share Posted June 12, 2010 Have a Holley 4412 #80 Jets... Plugs and tops of pistons (at last rebuild) look like it is running rich. Does running pump gas (Super) make any difference for jetting vs. racing fuel...Thinking the carb had race gas ran though it on a regular basis before I got it... Also if I lean out the carb. I assume it will run hotter as you lean it out, so do you take some timing out of the motor to keep it from overheating or does it really make a difference. Thanks in advance for any input... Marc Never in 20 years ran that fat. Put 76 jets in it and leave the timing alone. JMO Agreed ditto Link to comment Share on other sites More sharing options...
HiTech Posted June 12, 2010 Report Share Posted June 12, 2010 ok what about when you have a block off power valve you have to faten up the jets Is that correct??? then if you have the color of a paper bag color ,,is that good?? so what ya'll are sayin also if you run it too rich you could blow out the compression rings on all the pistons?? .... someone tell me why all the compression rings on all the pistons are broken ... the gap was right ,, piston to wall was right was it the fuel mixture??? shi//// I dont know running too hot of a plug??? what i suppose it is bored right .and done with a bore plate ..if you run it to rich ..my bet it would be washing all the lube off the pistons .... .. ussualy if you run too lean depending on the typ of piston you run .. it will burn the piston ..first .then get the rings ..and or head gaskets ...i look for grey powder particals on my pistons and head .... paper bag color or alittle golden if you will .is what i look for .. that maybe to fat for some ..or to lean for some ..but thats the way i have been do this for many years ..safe side you may say ...as for block off .if i run one .you ussualy have to go up 2 sizes .... Link to comment Share on other sites More sharing options...
jwmbishop Posted June 13, 2010 Report Share Posted June 13, 2010 someone tell me why all the compression rings on all the pistons are broken ... the gap was right ,, piston to wall was right was it the fuel mixture??? Are you the builder? Without watching your assembly I could not begin to troubleshoot an all rings broken. One or two I could ask questions about the differences between those pistons and the others, that would narrow it down some. Usually mixture does not hit them all at once - only the weakest ones - and there are other things to look at. the color and shape of the flame ring on the head gasket tells the most on lean mixture conditions -wet walls are obvious in the color and sheen of the ring wear against the cross hatch (hint - more cast iron "fills" the low spots when the mixture is lean or correct than does when the mixture is rich - the cast iron is washed out with excess fuel - so the wlls are greyer when wet) Link to comment Share on other sites More sharing options...
HiTech Posted June 13, 2010 Report Share Posted June 13, 2010 this has happened before ...if you or someone used a ring groover cleaning tool on the pistons .and cut the grooves to deep or even opened them wider . your rings will be or could be too loose ...or you have the wrong rings ... then correct gap wont matter ... that will break em ...i made that mistake a long long time ago ..... Link to comment Share on other sites More sharing options...
railer Posted June 13, 2010 Report Share Posted June 13, 2010 thanks gugs for all the help .. and what to look for now, my thought is the landings are just wore out and the gap was too wide . iwent with the bore dia but iguess i was wrong Thanks Link to comment Share on other sites More sharing options...
HiTech Posted June 13, 2010 Report Share Posted June 13, 2010 thanks gugs for all the help .. and what to look for now, my thought is the landings are just wore out and the gap was too wide . iwent with the bore dia but iguess i was wrong Thanks landings that the word i was looking for .. Link to comment Share on other sites More sharing options...
jwmbishop Posted June 14, 2010 Report Share Posted June 14, 2010 lands. Landings are for space shuttles. lol Link to comment Share on other sites More sharing options...
LMR21 Posted June 23, 2010 Report Share Posted June 23, 2010 FYI 4412 carbs come factory with 73 jets and to deviate more than three jet sizes either way does absolutely no good, there is a correct air/fuel ratio to maintain. and factory generally bases its test off sea level and 60 degrees F. humidity will change the numbers somewhat but very little. I might also add to little timing will also cause you headers to run cherry red and give the appearance of running lean. Now it might be wise also to check to see if the throttle bores have been modified this will change everything. NEVER EVER USE A DRILL BIT TO OPEN UP A JET. If you do the jet is now JUNK! they are machined flow orifices, not just holes in a threaded piece of brass. Link to comment Share on other sites More sharing options...
HiTech Posted June 25, 2010 Report Share Posted June 25, 2010 FYI 4412 carbs come factory with 73 jets and to deviate more than three jet sizes either way does absolutely no good, there is a correct air/fuel ratio to maintain. and factory generally bases its test off sea level and 60 degrees F. humidity will change the numbers somewhat but very little. I might also add to little timing will also cause you headers to run cherry red and give the appearance of running lean. Now it might be wise also to check to see if the throttle bores have been modified this will change everything. NEVER EVER USE A DRILL BIT TO OPEN UP A JET. If you do the jet is now JUNK! they are machined flow orifices, not just holes in a threaded piece of brass. when we use to run 5200 carbs .you could not get the jets you really needed .. i used to drill my jets in two to three steps ..tapered from the top to bottom ...at the size i was looking for ....worked out ok .but alway better to buy em if you can get em ..now we run the 4412 .. Link to comment Share on other sites More sharing options...
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