I'm tired of all the probs keeping my MagMar EFI tuned, on my '01 HD Ultra. I'm in the process of installinga 95" big bore kit, including heads.

I just heard that some people have bored the throttle body out and put in 42mm butterflies, replacing the 38mm ones.

Anybody done that, and know how good an idea it is?

 

42mm sounds good to me. i have a magnetti also pain in the *** until i discovered the secret two sealed screws at top center of backing plate. dig out sealant with sharp point tool. then adjust similar to airfuel mix screws on carb.i no longerrun a dfo. bike runs great finally no more pop andping.sounds like and runs like aharly should. good luck plus you will need to download stage3 for heads ,pistons to get proper ignition or update throttle body to s&s vfi also speeds performance plus has replacement throttle body for magnetti

 

Several shops do that mod. I had mine done back when the Road King was a 95" motor back in 1999 by BC Geralomy. I believe Hillside in NY does it too. It's a good mod, worth the 3-400 bucks.

 

My MM TB has the upgrade from to the two 42 mm throttle plate bores and has had the internal divider removed making it an open plenum rather then the two individual ports, like the newer Delphi style. To do this it was cut open from the bottom, the divider cut/ground out and then a plate was welded back in at the bottomproviding a flat floor and a larger, open plenum area. Don't know who did it, got from Ebay, but whoever did it was a good at grinding and welding.

 

Hey Dallonj, could you ellaborate more on "the secret two sealed screws at top center of backing plate"? Do the bored-out tb's improve the issues with the mag mar efi's(ping/pop on decel, hard start when hot,very abrupt slow down when letting off throttle,.... .etc)? Thanks in advance

 

Here's what I know.
I've had numerous discussions with tuners and builders, I have a BC Gerlomy bored throttlebody on a 98" build with a SERT on a MM bike.
Everyone I've talked to has no good opinion of the MM SERT, they all say the best way to gois to put on a Thundermax with a completely new throttlebody from Zippers.
I'm stready farting around with this thing and the ethanol in the Canadian fuel isn't helping.
If I'd have known this in the beginning, it would have cost more than the way I went but been worth it.

 

Just today I decided to try changing my 2001 Ultra Magnelli Marellit to a carb. I tried just about everything and spent $$$$$$. I had it bored out by Gerolamy ( in my opinion not worth the money ), cut out the center to make it open plenum ( mistake there)and now have a HP Inc. 51MM TB with Delphi injectors. I got to say the HP Inc. gave me about 10/10 on a dyno tuned with a SERT. My last DYNO was 117 HP and 121 TQ. With the Ultima 6 speed I have on it, a 80 mph cruise needs no down shifting. I should add I have a High Five A/C and Woods TW6HG cams. I can't be happier with the power but my gas mileage is in the tank. It seems it's just my bike because others running this set up are getting 40 mpg +/-. If I cruise at 80 mph two up riding I get around 28 mpg. So if anybody wants tobuy this HP Inc. 51MM MMXF TB I have let me know. I have had it on for about 4K miles and paid $1150 for it new.


The Other Ed
evhid1@hotmail.com

 

I'm guessing that a turbo charged 107" motor wouldn't matter/care if it was boosting through three 33 mm. corkscrews.
And my experiance says a 107 needs bigger holes but a 95"will get plenty of air through 38 mm.
Back in my shovel head play period,one of my nicest snappycrispy play builds was a 86" running twin 28 mm Mikunis round slides on single plenums<(with VERY large intake valves and some really nice flow work on the heads etc.etc..but then again I like Bendix and S&S B models too.
I guess my point is the air hole isn't the tuning problem,having said that,I'd make sure your guy doin the heads knows what your end result is.LOL
Tuning a 95" is no different than an 88".Good Luck.

 

After fighting the MM on my 01 (Yes, I had the bored TB) for a couple of years after building my motor, I finally switched to carb. Cheap, easy mod and the best mod ever for a MM bike. There are some complete parts lists around here and at VTF if you search. Mine ran about $600 complete but that included a new SE 44mmCV and Daytone Twin Tec ignition. It can be done much cheaper. Whole job took maybe 4 hours tops. I gues sthe 99&00 are a little more challenging because of the steel fuel lines inside the tank. Add another hour or two....

 

I have a bored marrelli that I gutted,you have to add a ton of fuel from just off idle because they get a lot more air than the stock ecm figures on....makes a ton more torque and better throttle response... Had similar results just by grinding a boost hole between the runners to improve vacuum signal and also gives the classic harley sound...(They don't suck long enough at idle to make any velocity...)

MM gets eratic idle as the throttle shaft bushings and plates wear,compounded by not having a throttle shaft seal on the TPS end...Think the rebuild kit comes with one that sits under the TPS...I made mine from a silicon rubber washer that sits under the coil in the old GM HEI distributors...Put that in,adjusted the throttle stop so the plates weren't binding and then brought the idle down with the idle bypass screws that are epoxied over... works great....

As far as bigger plates,I didn't really care about wot power,just wanted better bottom end...got both...

Great guys (and gal) at Horsepower Inc., they thought I was crazy when I talked to them....(but still wanted my money...lol)