idle sucks
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=4232
Printed Date: November-23-2024 at 3:51pm
Topic: idle sucks
Posted By: coreytread
Subject: idle sucks
Date Posted: July-19-2006 at 10:54pm
| ok just dropped the 351 reverse rotation in the 79, set the timing 8 degrees advance. went to the lake oh yeah I have a four blade prop from acme. the boat responds well, I ran it full throttle we toped at around 38. we noticed the idle was rough as in it shook the boat alot more than it should. So we loaded the boat up went to the shop changed out the elctronic ignition with a different one still the same I checked the firing order timing over and over, Ive got good gas new hoses plugs wires I even swaped the distributer from anotther identical engine still this rough idle. does anyone have any ideas Im going to work on it all day and would rather be drinkin beer with my lady friends all day cruisin. |
Replies:
Posted By: coreytread
Date Posted: July-19-2006 at 11:17pm
| oh yeah the prop is 13x12.50 .o80 |
Posted By: rmcdonald
Date Posted: July-20-2006 at 6:54am
|
Hi Corey
You have changed the timing, so you should adjust the carb to suit. You need to adjust you primary mixture screws, and probably your static idle What type of Carbie do you have. Below are some instructions for a tuning a Holley Carb. You can Download technical information from the holley web site on tuning carbs. IDLE MIXTURE NEEDLES: Idle mixture needles control the air/fuel mixture at idle. These have been preset at the factory and SHOULD NOT need any adjustments. However, if you feel that adjustment is necessary, you can use the following procedure to do so. When tuning the idle mixture, you’re actually tuning for the best manifold vacuum. Idle mixture needles are found on the primary metering blocks. If you change one idle mixture needle, you must change the other idle mixture needle by the same amount. Here are the proper steps for setting the idle mixture needles. 1. Attach the vacuum gauge to a manifold vacuum port on the throttle body (Figure 3). 2. Adjust each idle mixture screw (Figures 10 & 11) 1/8 turn at a time, alternating between each screw. Turn them equally, until you achieve the highest possible vacuum reading without adjusting the curb idle speed screw. Turn screws in to lean the mixture. Turn them out to richen the mixture. Figure 9 3. Now that the idle mixture is set, it may be necessary to go back and reset the idle speed using the curb idle speed screw, as shown in Figure 9. 4. If a vacuum gauge is not available, use a tachometer to obtain the highest RPM. Figure 10 Figure 11 ROUGH IDLE AND VACUUM LEAKS: If a rough idle persists after the engine has been started and the mixture screws adjusted, check for manifold vacuum leaks. These could result from unplugged vacuum fittings or a carburetor flange gasket that was torn during installation. Recheck for proper attachment of all vacuum lines and check the lines for cracks. If the manifold was changed, a manifold vacuum leak could occur at the cylinder head/manifold surface due to damaged gaskets or improper torquing. Frequently, manifold vacuum leaks occur from the valley side of the manifold. These are very difficult to detect, unless a discernible whistle can be heard. NOTE: In most cases, when rough idle occurs after a carburetor/manifold change, they result from manifold vacuum leaks similar to those described above. Assuring a proper manifold installation rather than assuming the carburetor is not functioning properly will ultimately save time. 10 |
Posted By: 79nautique
Date Posted: July-20-2006 at 9:04am
|
double check that you also don't have a small vaccum leak, like around the spacer or through the PVC hoses.
------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: coreytread
Date Posted: July-20-2006 at 9:00pm
| check this out mad my heart sink, we did a compression test this morning first cylinder 120 next cylinder 10 holy sh*t. next step pulled the heads cracked valves on cylinders 2 and 7. So I did what any man would do bought a set of GT40 heads thinking I could get some gaskets today but nope had to order some. So once again my motor is sitting on a stand. I needed to switch trannies anyway I noticed the prop spinning while in nuetral figured I would use my spare and get the other rebuilt. Im hoping the rings are ok and there are no other problems. I am positive the carb is set correcctly and almost positive the lower end of the engine is good. Im only going to run it until november than rebuild so hopefully the bottom end will hold up. The heads that went bad are bone stock and probably went bad from not using a lead additive. what you guys think? |
Posted By: SMay81SN
Date Posted: July-21-2006 at 1:05am
Hey Corey, sorry to hear your having problems with that motor out of the 81 As far as a lead additive, I should have stock in one of those companies...I have bought & put lead additive in that motor for 18 years...that motor was running strong in the 81 when you got. The GT40 heads should be great for it.------------- Scott http://www.correctcraftfan.com/diaries/details.asp?ID=1383&sort=&pagenum=1&yrstart=1991&yrend=1995 - Our 94 SN |
Posted By: coreytread
Date Posted: July-21-2006 at 2:55am
|
It had a slight miss when I picked it up from you actualy it was the same miss I just was hopiing it was timing and carb not the heads but I still saved alot of money either way. Ill send pics next week of a finished product, I thinkalmost everything in the boat is knew.
|
Posted By: GottaSki
Date Posted: July-21-2006 at 7:22am
Thats the biggest load of crap advice I've read in a long time. Its so inaccurate I don't know where to start. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
rmcdonald wrote:Posted By: 79nautique
Date Posted: July-21-2006 at 7:58am
|
Gotaski I agree with you never knew you could adjust the idle mixture screw on a FI motor. It's got to be pretty hard to do since there are none to adjust. Now a carb has them but I have never seen one on throttle body or multiport fuel injected motor, then again I don't believe corey is injected either. and in that case the procedure would work but they are not preset and should not be adjusted. If you want you engine to run right they have to be adjust anually if not by monthly depending on use. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: coreytread
Date Posted: July-21-2006 at 5:13pm
| Thanks guys, Im using the stock motor from the 81 I was lucky enough to get a set of gt40 heads from a proboss engine that had only 75 hours and something went wrong on the bottom end the guy ordered a whole knew engine instead of rebuilding. 79nautique you seem to be pretty good with these engines do you think the gt40 heads are the correct choice and will I gain 40 hp or is that being over optimistic. |
Posted By: TRBenj
Date Posted: July-21-2006 at 7:53pm
|
40 hp should be about right coming from stock 351w heads- the GT40's were the primary difference between the 240 horse base motor and the 285 proboss.
There are other choices out there, but GT40p's are really the only other iron head that I know of that will give you better performance than the GT40's- and the difference shouldnt be huge. If you got a good deal on these low hr heads, I dont see how you can go wrong. My dad made the switch on his '92 and saw a nice improvement. ------------- |
Posted By: coreytread
Date Posted: July-22-2006 at 12:05am
| Thanks for the infothese heads are directly off a proboss and look brand new. Im paying 1k for them with no install fews all gaskets included. |
Posted By: rmcdonald
Date Posted: July-22-2006 at 7:39am
|
Hi GottaSki
If you are going to sl*g me off on this forum, at least have the decency to say what is wrong with the information that I posted. If you read my post: I asked what type of Carbie Corey was using. The information that I posted about tunning was information supplied from the Holley web site for a Holley 4010, purely as a guide. There is nothing wrong with the tuning information. The only information that I did not agree with is the sentence about adjustments being factory preset and not needing to be adjusted. |
Posted By: GottaSki
Date Posted: July-22-2006 at 9:16am
|
Then you are in err. And Grow some skin. What else do you call crap advise?
You prematurly ejaculated garbage advice for a carb he doesn't have when you were not sure which carb he has. Who's doing corey the disservice? And you basically advised how to dial in a great off-idle hesitation and poor hot starting. Best vacuum is a myth unless it is performed in gear. His carb has air screws. they control air. hence the name. Closing them richens the idle mix. Your instructions are azz backwards. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: rmcdonald
Date Posted: July-22-2006 at 10:28am
|
GottaSki
You want me to grow some skin, May be I could borrow some of the foreskin that you wear on your forehead What information have you actually provided? I love it,you are such a expert. You dispute the info on tunning a Holley carb distributed by Holley If Corey does not have a Holley carb then so what he can ignore the info. |
Posted By: GottaSki
Date Posted: July-22-2006 at 10:47am
I'll ignore most your mouth-foaming...
Yes. Wrong information from a good source is still bad information. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |