Hesitation; fuel starvation?

[Rich K]

Hi, thought I would share a problem occurring recently on the drophead 7. So basically I have been experiencing some hesitation from the engine whilst on the move, especially but not exclusively under acceleration. My gut says it is a fuel problem but I guess it could also be ignition related. I have checked some obvious things; the spark plugs look good with a nice tan deposit and the ignition leads are all giving the expected resistance reading when tested on my multimeter. The timing is correct at 10 degrees before tdc and the points gap/dwell angle is also good. All ignition components are fairly new including dizzy cap. Low tension connections to coil are also good. Methinks therefore it is not an ignition issue so I move onto checking fuelling issues. So I strip the carbs down and clean off any deposits with carb cleaner. The float chambers have fuel in them and the floats are ok. There is a small ridge worn into the needle valves but not excessive. I then move onto the fuel pump and removal of the lid reveals a shocking amount of debris and silt partially blocking the onboard filter. Strangely at this point there is little fuel flow from the rubber fuel pipe leading to the pump. I clean up the filter and reassemble before taking the car out for a test drive. Damn it the hesitation is still there! I circle round back home and stop the car only to smell fuel. Opening the bonnet reveals a steady flow of fuel from the connection of the rubber pipe to the pump. It seems that a previous owner had replaced the pipe with some none fuel resistant stuff and this was now bloating and cracking. Damn it! I know that I have some spare fuel hose somewhere in the garage but play time has run out for the day. The car is now back in the garage with a bolt temporarily plugging the leaking fuel hose. Hopefully I will find time to fix this and test drive the car during the week to see if a replacement pipe can cure the problem.
Rich.

[John_C]

A very common cause of this problem is debris in the fuel tank due to water getting into the tank. As you're going to need some fuel pipe anyway, purchase enough to run the car from a jerry can in the cockpit and then see if you still have the problem.

[Hasbeen]

There is a lot of poor quality fuel hose around wearing good brand names. I bought some Gates fuel hose a while back that cracked in just 12 months. My hydraulic bloke told me he only uses any fuel or hydraulic hose stamped Made in America, to avoid Mexican or Asian made stuff.

If your fuel tank has not been replaced or treated it will have a lot of rust inside it. Most have rusted through in the last few years. It does not require rain, condensation will put enough water into your tank to destroy in under 30 years.

Clean out your tank, & if you have an inline filter replace it, while you are mucking with the hoses.

With all this, I has a similar hesitancy in my 7 for a couple of years. I thought I had fixed it a number of times, but the Lumenition electronic ignition finally failed completely, finally pin pointing the actual problem.

Hasbeen

[Rich K]

Thanks for the responses. John_C thanks for the tip, I will try that if simply replacing the section of hose doesn't do the trick. Hasbeen that's a good point, I will try to source some decent quality hose. Any idea what the internal diameter should be? As a side note, I already cleaned out the tank and used POR15 Tank Sealer some months ago so hopefully there will be no more crud coming through from the tank to block the pump filter. I will also add an inline filter for extra security. I think the old hose was probably collapsing and leaking for some time which no doubt wasn't helping the situation.
Rich.

[busheytrader]

Hi, I had fuel starvation due to the tank rusting from the inside out and clogging the fuel pump's filter with an ultra fine orange powder (rust). Hesitation would occur under gentle acceleration. I'm not sure how fine that filter mesh but if there's no crud in the fuel bowls then hopefully it's not in the carb's.

[FI Spyder]

I would think most if not all fuel hose would be alcohol resistant (do you have alcohol in UK?). There are hoses that are for vacuum line and hoses that are for fuel and should not be interchanged. Place of manufacture may well make a difference.

[Rich K]

I got hold of some proper 8mm id fuel hose today so will fit this later in the week when I get time. I already stripped and cleaned out the carbs. I did find some fine black particles in the jets that looked like broken down rubber from the old hose which must have been fine enough to pass through the filter mesh. Hopefully there will be no more hesitation and no more smell of fuel!
Here is a picture of the old fuel hose showing how it has degraded from the inside out. It wa so bad when I took it off that fuel was actually sweating through the wall of the hose.

[Rich K]

Just got round to fitting a new old stock condenser that I purchased off EBay. Happy to report that the car is now running sweetly again with none of the hesitation previously experienced.
Rich.

[saabfast]

I would recommend fitting electronic ignition. The points on these seem to need regular resetting and are a pia to get to. I fitted the Aldon ignitor system (cheapest from Retro Rockets US site but supplied from UK warehouse) and condensers do not seem to last forever like they used to. Very easy to fit and I have not looked in the distributor cap for the past years since fitting, runs smoother too.

[Rich K]

Yes, fitting electronic ignition is definitely a good upgrade for the 7. My red DHC has the piranha system fitted and this has proved trouble free over a long period since being installed. Trying to set the correct points gap on a 7 distributor is surely one of the most frustrating and fiddly jobs there is.