Timing advice

[FastFisher88]

Hi,

I embarked on a 90 to 140ish conversion with a 1987 88 and 1976 135. What I've done so far:

-swapped heads
-cut webbing at bottom of block for exhaust
-installed exhaust filler plates and bubble back
-swapped in the 1 5/16 carbs which I fitted ports to keep solenoid choke, removed the choke flaps.

Jetting is tad on the rich side which ill keep. Trying to tune timing since full advance by the book is 28deg for the 88 and 20deg for 135. Later 140 crossflows were 28.

If someone knows could save me some trouble, do I back off timing to match 135 or keep around 88 specs? Took it out last weekend with adv set at 18 and while it ran decent i basically matched stock 88 performance (48mph @5000rpm with 23p). This is on a 16ft fiberglass bass boat with a pad.

Not sure why the difference in specs other then ignition systems? Both 140 and 135 use higher compression heads although 140s were bit looser.

Will port it to 135 specs overwinter when I have time. Just want to do some fishing now. Thanks.

 

[racerone]

The 88 / 90 HP blocks had smaller intake ports I believe.-----Did you open them up ?

 

[FastFisher88]

I have not yet, had a leaking exhaust gasket and po helicoiled a spark plug that was letting go so I just swapped parts for now. Will port 88 this winter. I also replaced the thermostats and installed a telltale on the 135 bubbleback.

 

[Faztbullet]

Did you machine the exhaust chest when you installed fillers in exhaust?

 

[racerone]

I post #1 he indicates this was done.----Have done that procedure myself.

 

[FastFisher88]

Only procedure remaining is to port block to the specs off the 135.

Just curious why the different timing specs 135 20deg vs 140 xflow 28deg? I know power packs were different but not sure what exactly accounts for this.

Trying 22deg today using 93oct. I'm using reeves method setting timing at cranking and adding 4deg(set at 18 so running wot should be 22) Idle is set at 4deg.

 

[racerone]

Where did you find the 20 deg spec ?----What manual ??----Is it possible that the 20 degree is a mistake / typo ?---I might have a 135 with a decal that has the timing info.

 

[FastFisher88]

I have a third party service manual that list timing specs for all years/models. Google seems to back it up.

 

[Faztbullet]

I post #1 he indicates this was done.----Have done that procedure myself.

I was asking if he milled the exhaust chest even with the fillers..You cant just slap a set in as got to be flat all the way across..
And why go thru all the effort to tear it back down and try to port it and only get 115HP at prop??? Better to get a 140 looper if wanting to go fast.

 

[FastFisher88]

Yes exhaust is flat didnt have to take much off at all was surprised. Boat can't handle anymore weight so no looper. I picked up the 135 for $100 but didn't have bottom or power packs which I didn't need anyway.

This is just a cheap project since I found the 135, would have preferred a 140 crossflow but good luck finding one here thats even capable of running.

I'm not looking to go 80mph just enough to swing the 23p. Wouldnt be to comfortable going over 60 i reckon.

Everything is good just figuring out if I can time it close to 28 or leave it at 20. Ran with 22 today ran good got to 50mph with bad wind and chop. Tach is giving me grief. New rectifier but still readings climb out of control after approx 4k rpm (ie guage reading 7k while engine is around 5k).

 

[FastFisher88]

Fazt I'm also aiming for 130ish at the prop. Have boysen reeds and intake wedges installed. Prop rated 115 didnt have the high comp heads or intake fillers i believe. Should account for couple extra ponies.

 

[Faztbullet]

Takes a lot of work, porting ,compression to get those extra ponie and you wont get em thru bolt on parts.

 

[FastFisher88]

Yup got that. Everything is done except porting. Planning on new rings if the piston bore clearance still in spec. Bores were still in nice shape when I swapped the head. Block was rebuilt since there's another number on the vin stamp, just not sure how long ago.

Just curious if anyone can explain why the difference in timing specs. Think ill try 24 next still no sign of deto.