1974 135hp fuel mileage problem

[wolfe1974]

hello,
this is my first post so i hope i can make sense. I just purchased a 1974 17ft chrysler boat that has a 1974 135hp evinrude on it. the engine runs well starts good. the problem is that i went for a check ride on sunday and went approx 3 miles ( not all of it at wot but may be 1/2) and used 5 gallons of gas. the boat with motor weighs 1600lb and i had 600lb of people on board. i previously owned a 1972 17ft mark III century v drive with a 340 v8 and could go all day on 10-15 gallons, I was hoping this boat would be on par with that type of consumption. is that normal and if not what can i do to help economy. it has the surface type plugs in it right now, would changing to "regular" type plugs help? or a decarb with seafoam? any suggestions would be appreciated

 

[jonesg]

Re: 1974 135hp fuel mileage problem

2 strokes consume 10% of the hp rating in gals per hr.
135hp = 13 gals at WOT per hr.

A 75hp might be enough to push that boat if it isn't full of wet foam.

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

so what can i do to help economy. how do i tell if the surface gap plugs are "bad" this is my first look at this type of plug so i really dont know what to look for.

 

[DJ]

Re: 1974 135hp fuel mileage problem

so what can i do to help economy. how do i tell if the surface gap plugs are "bad" this is my first look at this type of plug so i really dont know what to look for.

Look for rounded edges on the center electrode and the surrounding ring. If they are not sharp/crisp, you should replace the plugs.

A 135 Crossflow V-4 was never accused of being "thifty".

 

[emdsapmgr]

Re: 1974 135hp fuel mileage problem

Those 135's great engines, but are gas hogs. They have huge high speed (.069) jets in the carbs to make hp. The best fuel economy for those engines is at approx 3/4 throttle. You can pull back the throttles off till the carb butterflys close slightly, but the timer base stays at max timing. That's about 3/4throttle. Make sure the engine is propped correctly-that will also affect fuel economy.

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

will decarbon with seafoam help or is that just something to do when it runs rough

 

[rtek816]

Re: 1974 135hp fuel mileage problem

37 years young. Is the 1600 lb boat spec or actual. Mileage goes down with weight. Might have 3 or 4 more people sleeping underdeck.

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

I am going to the scales to weigh it to get an actual weight.

 

[Fed]

Re: 1974 135hp fuel mileage problem

5 Gal for 3 Miles, you've got a hole in your tank or you measured wrongly.

On a serious note I once tilted my boat way up and drained the tank via the fuel line then added 5 Gals which should have been ample for the short shakedown cruise I went on.
I ran out on the way back????
Turned out my fuel pickup in the tank doesn't get the last 2 Gals out when the boat is level.

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

I am going to replace the plugs. should i stick with the surface gap plugs or go with a standard type plug?

 

[wilde1j]

Re: 1974 135hp fuel mileage problem

Decarbing won't help fuel economy. I had a '73 135HP that did OK @ ~ 3800 to 4000 RPM. Either surface gap or std gapped plugs are fine, but surface gap plugs will last much longer, but don't troll so well. As I recall UL77V or L16V was the surface plugs for that motor.

 

[emdsapmgr]

Re: 1974 135hp fuel mileage problem

There was an OMC service bulletin (whose number I can't recall) in the mid 80's. Stated that some dealers were installing J-gap plugs in the crossflow engines at the time. Further, that this could cause detonation in the engines. If the factory found those J-gap plugs in a warranty engine with a failed powerhead, that they would deny warranty. The surface gap UL77V Champion plugs will work just fine in your engine.

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

ok I had read on here that the correct plug was a ql77jc4 it was on a post for a 1976 engine but i thought that my 1974 was basically identical. so i bought the j type plug. i havnt installed them yet. what is the right thing to do.

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

there was a post by Joe Reeves that said the correct plug was QL77JC4 (for a 1976 engine but i uderstand that the 1974 in basically the same)which is a j type plug. so i bought those but havnt installed them yet. what is right to do?

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

anyone?

 

[emdsapmgr]

Re: 1974 135hp fuel mileage problem

OMC issued a follow-up service bulletin in the 93 timeframe-it was posted on an earlier thread. Seems to overrule the early one. Looks like the resistor j-gap plugs are an acceptable substitute.

 

[yoster]

Re: 1974 135hp fuel mileage problem

Guys - there's more wrong here than an engine issue. 5 gallons in THREE miles? Yeah, no spark plug replacement is going to fix that..

As others mentioned.. this was either measured wrong or you really do have a leak somewhere. If that much gas was going through the engine, it wouldn't even run.. it would flood out.

 

[wolfe1974]

Re: 1974 135hp fuel mileage problem

well I did some more testing and the fuel consumption is OK. I was mistaken in the initial distance that I traveled. I had the boat out last weekend and it did OK on the fuel. I will change the plugs because PO said he didnt do a thing to the boat. so I am just going through the thing to get it back in shape! I was just unsure of what plug to put in. most of my boating is pulling a tube for the kids. So I am not going from A to B just riding around in large coves on the lake. it is hard to tell how far i go but i used 12 gal and boated for 4 hrs or so of stop and go tubing. i was also wondering on these engines it looks like the plug wire is part of the coil. so is there a way to change just the plug wire and not the whole coil? thanks again for the help!!

 

[emoney]

Re: 1974 135hp fuel mileage problem

I don't know how much I agree with that, Yoster. I"ve got a Crossflow 140hp and it wouldn't shock me if it used 5 gallons in 3 miles. This motor of mine has BIG loss in fuel economy when the RPMs are kept above 4500. It doesn't mind running up there, matter of fact it likes it, however, it also has quite the drinking problem in that range too, and I know for a fact my boat is dry as a pin because it's been redone. Now, I spend all of my time in the Gulf and we've been running in quite a chop as recent, so I'd think a smooth lake would be better. When I keep mine down around 3700-4200, which on my boats equates to about 28-30mph, she seems to do a LOT better fuel wise.

 

[levi_tsk]

Re: 1974 135hp fuel mileage problem

my mechanic said that its a pain in the butt to get those surface gap plugs to run right hes an older guy and he worked on these engines when they were new and he said even then they sucked he told me the same thing joe said and that is to run the QL77JC4 unless of course that i liked meddling with spark plugs every other trip he also said that the L77JC4's are an alternative and that the QL's would be goood if i had any onboard electronics from what he was telling me the j plugs have lower heat range so theres no real way that you can do any damage by running em
my 81 140 is deffinitely a thirsty fellow also
and a fourstroke v8 i/o will burn far less gas than a two stroke outboard