Idle quality of blower motors
10-30-2002, 05:01 PM
#1
Guest
Posts: n/a
Idle quality of blower motors
Want some input on idle quality quirks of blower motors. I have a 8-71 intercooled 540 with demon carbs and locked out timing. With the locked out timing and demon carbs (changed both at the same time), the idle quality greatly improved. I now have a neutral idle rpm of about 950 with no surge. It pulls out of the hole with no poping. My main problem now is that it will always die when put into gear. I have to grab the throttle with my left hand and advance it slightly as soon as I shift with the right. This is a little hairy as usually it is coming off the trailer and I don't exactly want to pull the rear of the boat down further while backing up. A high pitch prop doesn't help matters, I'm sure.
I forever was *****ing about the huge surge that I used to have. Now that it is gone, the hydraulic steering behaves at idle, but it sucks that I have to do a dance to get it into gear. Coming back to the marina falling off plane, it will idle in gear with the boat moving, but even that is pushing it, as it is gradually slowing down..
This engine has a solid cam and is running around 8-9lbs boost. I have been running 100ll gas lately. Do all roots motors at this boost level have this issue? The idle rpm doesn't bother me too much, if it wouldn't sputter when put into gear.
The locked out timing keeps the advance mechanism from jumping all around at idle, amplifying any surge. I thought about the idea of running 1/2 timing at idle and possibly throwing the rest in with a switch on the gear selector. Kind of like the old air conditioning soleinoids, except with timing instead.
What have other done about this, and do they experience this?
Thanks.
I forever was *****ing about the huge surge that I used to have. Now that it is gone, the hydraulic steering behaves at idle, but it sucks that I have to do a dance to get it into gear. Coming back to the marina falling off plane, it will idle in gear with the boat moving, but even that is pushing it, as it is gradually slowing down..
This engine has a solid cam and is running around 8-9lbs boost. I have been running 100ll gas lately. Do all roots motors at this boost level have this issue? The idle rpm doesn't bother me too much, if it wouldn't sputter when put into gear.
The locked out timing keeps the advance mechanism from jumping all around at idle, amplifying any surge. I thought about the idea of running 1/2 timing at idle and possibly throwing the rest in with a switch on the gear selector. Kind of like the old air conditioning soleinoids, except with timing instead.
What have other done about this, and do they experience this?
Thanks.
10-30-2002, 05:20 PM
#2
Guest
Posts: n/a
I have holley 950's with 4 corner idle adjustments. If the motor stumbles and dies when going in gear try richening the idle jets slightly. If the motor excessively lopes at idle try leaning the idle jets. Thats what I've been told and it works for me everytime.
10-30-2002, 05:39 PM
#4
Registered
Join Date: Jan 2001
Location: hamilton ,ohio USA
Posts: 99
Likes: 0
Received 0 Likes
on
0 Posts
502 w/bm 250, 2x 750 holleys, 8 lbs boost. timing set at 29* all the time. Carbs have been boost referenced, idles like a dream, in and out of gear. I did have some problem early on with dieing in gear, slightly richening idle mixture screws took care of it though. But I'm probably not running as big a cam as you are,crane 731, good luck
10-30-2002, 06:04 PM
#5
Registered
Richer A/F mixture should help. Are you getting good reactions when you turn the idle mixture screws? If not you may need to pull the carbs and see how much of the idle transfer slot is showing. If your primary plates are tilted to much there will be little to no response when your mixture screws are turned. You may need to back off the plate angle and drill some holes in the butterflies. This will cover up some of the idle transfer slot and give you the ability to use your mixture screws. On holleys only about .040" of the transfer slot should be showing. It works great on NA motors. On blower motors??? How fast ya runnin? With the new huffer you are probably in the 105 MPH range.
10-30-2002, 06:13 PM
#6
Registered
Join Date: Sep 2001
Location: Houston, TX, USA
Posts: 2,287
Likes: 0
Received 0 Likes
on
0 Posts
Got 540BBC stage 4 procharger with the crane 139741 cam 1.36 gears & 30" bravo prop. Motor idles at 850 & 550-600 in gear when motor is warm, when cold coming off of trailer I need to feather the throttle to get it off trailer to keep motor from dieing. Once warm is OK.
I would look & see if while motor is idling if you can see fuel coming out of booster. If so you will need to drill hole in throttle plate to let more air to engine at idle without having the idle adjusted up to high.
I would look & see if while motor is idling if you can see fuel coming out of booster. If so you will need to drill hole in throttle plate to let more air to engine at idle without having the idle adjusted up to high.
10-30-2002, 06:53 PM
#7
Registered
Brad:
You should be able to get the idle RPM a touch lower, but either way it sounds like the butterflys are out of position for it to be stalling when you're putting it in gear. It should be pretty simple to fix this problem, by doing the following.
1) Remove the carburetors, and inspect to see how much transfer slot you have expose below the butterflys right now. (generally we'd like to see about .020")
2) Find which ever set are open the furtherst amount, and now open all of your butterflys to this amount
3) Re-install the carburetors, and start the engine up on a hose.
4) Once the motor & oil get up to full operating temp. you can back off on all 4 of the idle speed screws the same amount to get the RPM to the desired level.
5) Now go back through your idle mixture screws, and re-do the idle speed screws one last time (remembering that you want to keep them open the same amount)
6) If this doesn't fix your problem give Marv a call at The Blower Shop, or me directly at (706) 864-8544 Ext.125
Doug
Head of technical services Barry Grant Inc.
You should be able to get the idle RPM a touch lower, but either way it sounds like the butterflys are out of position for it to be stalling when you're putting it in gear. It should be pretty simple to fix this problem, by doing the following.
1) Remove the carburetors, and inspect to see how much transfer slot you have expose below the butterflys right now. (generally we'd like to see about .020")
2) Find which ever set are open the furtherst amount, and now open all of your butterflys to this amount
3) Re-install the carburetors, and start the engine up on a hose.
4) Once the motor & oil get up to full operating temp. you can back off on all 4 of the idle speed screws the same amount to get the RPM to the desired level.
5) Now go back through your idle mixture screws, and re-do the idle speed screws one last time (remembering that you want to keep them open the same amount)
6) If this doesn't fix your problem give Marv a call at The Blower Shop, or me directly at (706) 864-8544 Ext.125
Doug
Head of technical services Barry Grant Inc.
Last edited by RumRunner; 10-31-2002 at 05:37 AM.
10-30-2002, 07:00 PM
#8
Registered
Join Date: Oct 2002
Location: GUN LAKE MICHIGAN
Posts: 80
Likes: 0
Received 0 Likes
on
0 Posts
WE HAVE HAD THE SAME PROBLEMS YOU DESCRIBED ON STREET AND DRAG RACE CARS USING DEMON CARBS. B.G. MAKES IDLE AIR BLEED KIT TO CORRECT THIS PROBLEM. ITS NOT TO HARD TO INSTALL THE NEW BLEEDS, JUST DON'T DROP THEM DOWN THE CARBS. ITS BEST TO REMOVE THE CARBS AND INSTALL THE KIT ON THE BENCH!!! CALL DEMON @ 706-864-4712
10-31-2002, 10:33 AM
#9
Guest
Posts: n/a
Thanks for all the replys.
Many of you hit on things I have done. When I got the carbs, I set all the butterflys equal and always move all idle screws, so that the transfer slot exposure will be at a minimum. The motor idle is extremely sensitive to idle A/F adjustments. I am probably tuning to the extreme, trying to get all surge out of the idle, something I was not able to do with the prior Holleys (most likely due to my inexperience). I can turn one (1) ! idle mixture screw less than an eigth of a turn and a little surge begins. Will I need to have some surge to have an idle mixture that will be a little more tolerant of load? Does this degree of sensitivity to mixture sound excessive?
10-31-2002, 10:38 AM
#10
Guest
Posts: n/a
Hey wette,
After having so many problems getting the drive gears installed correctly and having the u-joints come apart, I'm quite shy about wringing it out. I felt a little vibration in a right turn at about 60mph. I have always felt some since stepping up to 27 and then 29 mirages. But after the u-joint fiasco, I'm a little paranoid. Boat now has a new transom assembly, u-joint assembly and the drive has been freshened and engine aligned. There shouldn't be anything but the prop causing this, but it has me jittery. Need to try someone's low pitch prop to test the theory.
After having so many problems getting the drive gears installed correctly and having the u-joints come apart, I'm quite shy about wringing it out. I felt a little vibration in a right turn at about 60mph. I have always felt some since stepping up to 27 and then 29 mirages. But after the u-joint fiasco, I'm a little paranoid. Boat now has a new transom assembly, u-joint assembly and the drive has been freshened and engine aligned. There shouldn't be anything but the prop causing this, but it has me jittery. Need to try someone's low pitch prop to test the theory.
